Previously the module path was a relative to the install
directory. With this patch the CMake package configuration file contains the
full path and the macros are found.

This branch adds support for a new, implicit build mode to
BCRSMatrix and moreover improves error handling and the
build stage system used during matrix construction.

* feature/new-bcrsmatrix-buildmode: (35 commits)
  [BCRSMatrix] Fix a documentation typo
  [BCRSMatrix] Some small fixes to allocation and deallocation in implicit mode
  [BCRSMatrix] Prevent against accidental double allocation of row array
  [BCRSMatrix] Clean up deallocate() a bit
  [BCRSMatrix] New observer buildMode() to get at the currently active build mode
  [BCRSMatrix] Adjust existing build stage checks to new enum values and semantics
  [BCRSMatrix] Prevent changing the implicit build mode parameters after matrix construction has started
  [BCRSMatrix] Improve logic in setBuildMode() to correctly handle new implicit mode
  [BCRSMatrix] Prohibit copying into / out of partially built matrices
  [BCRSMatrix] Add checks against calling arithmetic operations on partially built matrices
  [BCRSMatrix] Make sure to always initialize all data members in constructors
  [BCRSMatrix] Introduce new build stages notAllocated (aliased to notbuilt) and building
  [BCRSMatrix] Export the type of the CompressionStatistics object
  [BCRSMatrix] Improve error reporting in BCRSMatrix
  [BCRSMatrix] Add safeguards for implicit mode to operator[]
  [BCRSMatrix] Improve error handling for implicit build mode parameters
  [BCRSMatrix] Fix typo in setImplicitBuildModeParameters
  [BCRSMatrix] Update maximum number of row entries in compress() on the fly
  [BCRSMatrix] Avoid off-by one iterators in compress()
  [BCRSMatrix] Rename BuildModeWrapper to ImplicitMatrixBuilder and add an extended constructor
  ...

- Don't do anything if we're in build stage notAllocated
- Reset pointers to nullptr after deallocating
- check whether rows have been allocated before accessing them

[BCRSMatrix] Prevent changing the implicit build mode parameters after matrix construction has started

Valgrind was complaining about using unitialized values in some places...

notbuilt) and building

Right now, some build modes reuse the same build stage value across
several actual stages. This patch splits the notbuilt stage into
notAllocated and building, avoiding that ambiguity.

- Introduce new exception BCRSMatrixError and use it throughout
  BCRSMatrix
- Introduce new exception ImplicitModeOverflowExhausted, which is thrown
  by compress() for the implicit build mode. Also improve the error
  message for that exception to really help the user understand the
  problem signalled by this exception and how to remedy the situation.

This patch adds checks to make sure the user has actually set valid
parameters before trying to allocate the matrix in implicit mode.
We use a negative value for the overflow fraction as an indicator for
this.

As part of the cleanup, this patch also makes sure that avg and
overflowsize are always initialized to a well-defined value.

This was obviously never tested - don't try to assign the overflow
fraction to the map holding the overflow entries...

We iterate over all rows anyway, so avoid the additional loop.

compress() uses iterators that are off to enable a *(++it) = ... idiom,
which already confuses me right now. That confusion will only be worse
when I look at the code again in half a year, so let's clean that up
right now.

ImplicitMatrixBuilder now has some more documentation and a second
constructor that takes all required arguments for setting up a matrix in
implicit build mode. So you can now create an ImplicitMatrixBuilder
directly on top of a default-constructed BCRSMatrix.

- Don't needlessly specialize the wrapper, we can still do that
  we we encounter the need for it.
- Add some doxygen documentation.
- Clean up formatting.

This one slipped through the cracks when renaming the build mode...

OS X does not support feenableexcept(), so don't try to call it.
Enabling FP exceptions wouldn't really help anyway because that only
works for the FPU, but all floating point operations on 64-bit OS X
are done using SSE / AVX, which does not support FP exceptions.

The sparsity pattern of the matrix is defined implicitly while
assembling the matrix.

call the matrix "Matrix" instead.

The given implementation only makes sense for a BCRSMAtrix, thus it should
only be used for such. This is in line with ISTLs general coding style.
Also added bit of doc.

This wrapper allows code to use the BCRSMode in implicit
build mode with the default operator[][] API during the
initial build stage.

Add the tests already present in CMake, that use UMFPack instead of
SuperLU as a coarse level solver.

Mpi flags were not added to pamgtest if parmetis was not present.
This is of course unwanted behaviour. The patch adds pamgtest to
the mpi tests (in addition to being part of the parmetis tests)