If an iterator facade (like entity iterators) wants to allow the
embedded implementation to return either an (internally stored)
reference or a temporary object and expose these two behaviors to enable
performance optimizations, operator->() needs special handling: If the
implementation returns a reference, operator->() in the facade can
simply return the address of the referenced object, but if the returned
object is a temporary, we need to capture and store it in a helper
object to make sure it outlives the member access.

This patch adds a little helper function that tansparently handles both
cases.

These check whether std::call_once() works and provide a helpful error message
if it does not.  They should be used in any code that uses std::call_once().

Call once may not work if one forgets to _link_ with -pthread (or similar
options).  The nasty think about this is that linking still succeeds, so this
can only be detected at run time.  We cannot (in general) run compiled
programs during configure, since we may be cross-compiling, so whatever we get
from configure is at best a guess.

Even if configure detects the necessary flags correctly, there may still be
errors in the build system such that the executable is linked without them.

The reason to provide such a facility is that the bug is quite difficult to
debug when it appears.  The error message is mangled due to a different bug,
and is quite unhelpful anyway.  And then there is the fun with weak symbols...

IteratorRange is a cheap, throwaway container to implement support for
range-based for loops if the underlying containers doesn't provide
standard begin() / end () methods.

DUNE_FINAL is a helper macro for C++11 and should be placed in
std, where now all compatibility has to be placed.
Beautify Doxygen documentation.

These headers were moved in Dune 2.3.

This implementation of an IdentityMatrix does not hold any data. It
implements a reduced version of the DenseMatrix interface including a
standard C++ cast operator to a Dune::FieldMatrix. This code illustrates
the new forward capabilities of DenseMatrixAssigner.

Thanks to Tobias Malkmus for the heads-up.

The majority of developers favor individual headers for (emulation of) C++11
features over collecting them in a single header cxx11.hh. This patch
renames cxx11.hh to constexpr.hh and moves it into the subdirectory std.
This is the place most developers would like these headers in (see
http://users.dune-project.org/doodles/4).

As decided on the developer meeting in Aachen, we support (but do not
rely on) the C++11 keyword constexpr. This patch adds an m4-check for
constexpr and a header (cxx11.hh) defining a macro DUNE_CONSTEXPR either
as constexpr or empty (depending on the compiler support for it). It is
then used in FieldVector and FieldMatrix on size, rows, and cols.

[[Imported from SVN: r7379]]

[[Imported from SVN: r7124]]

Add basic support for hashing using Dune::hash

This patch introduces the functor Dune::hash in a similar manner to
other C++11 functionality by importing the definition from namespace std.

Apart from that, the patch also provides some basic functionality to simplify
making user-defined types hashable, in particular functions for combining hashes
and hashing iterator ranges as well as a mechanism for defining the struct
specializations required by std::hash and std::tr1::hash in the correct namespace.

The current implementation will first try to use std::hash and, if that fails,
attempt to fall back on std::tr1::hash. If that is not available either, hash
support is disabled as there is no homegrown fallback for now.
The extension mechanism will register the type with both std::hash and std::tr1::hash,
if available. This should make it possible to use unordered_{set,map} from both C++11
and TR1 without having to specify a custom hasher.

Kudos to Steffen Müthing, see FS#1192

[[Imported from SVN: r7065]]

Capabilities to compute eigenvalues on non-symmetric matrices
Code contributed by Arne Morten Kvarving.

[[Imported from SVN: r7061]]

[[Imported from SVN: r7042]]

There are lots of power implementations all over our code.
This is the first step of some cleanup.  It moves the class Power_m_p
from misc.hh (like who's ever gonna find it there...) to a separate
header power.hh.  Other implementations will be collected there as
well, if appropriate.

With the patch, including misc.hh will issue a cpp warning that people
who include misc.hh only for Power_m_p should now include power.hh
instead.  This is not great, because it also affects people who include
misc.hh for something else.  Bear with this for a while; I couldn't
think of a better solution.

[[Imported from SVN: r7032]]

rename files... remove underscores

[[Imported from SVN: r7012]]

[[Imported from SVN: r7009]]

[[Imported from SVN: r7006]]

[[Imported from SVN: r6999]]

It is used from the dune-geometry module (see FS 1180).

[[Imported from SVN: r6995]]

[[Imported from SVN: r6930]]

[[Imported from SVN: r6925]]

SmartPtr< T > is similar to shared_ptr< T > in its intention. However, it
demands methods addReference and removeReference on the object it points to.
Actually, you could implement shared_ptr< T > through a
SmartPtr< RefCountWrapper< T > > and a few cast operators.

[[Imported from SVN: r6919]]

[[Imported from SVN: r6902]]

[[Imported from SVN: r6886]]

- add dotproduct for basic data types
(thanks to Matthias Wohlmuth)

[[Imported from SVN: r6862]]

dune-geometry.

[[Imported from SVN: r6796]]

[[Imported from SVN: r6795]]

[[Imported from SVN: r6596]]

[[Imported from SVN: r6557]]

[[Imported from SVN: r6544]]

[[Imported from SVN: r6487]]

[[Imported from SVN: r6456]]

[[Imported from SVN: r6453]]

[[Imported from SVN: r6436]]

[[Imported from SVN: r6403]]