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...

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.

use FieldTraits to determin the return type of the norm methods

(kudos to Elias Pipping for the patch)

[[Imported from SVN: r1910]]

Because it does not currently have any measurable benefits.

[[Imported from SVN: r1769]]

[[Imported from SVN: r1768]]

[[Imported from SVN: r1767]]

Improved it such that placement new is only called when necessary.

[[Imported from SVN: r1757]]

[[Imported from SVN: r1737]]

[[Imported from SVN: r1736]]

[[Imported from SVN: r1608]]

[[Imported from SVN: r1570]]

[[Imported from SVN: r1537]]

[[Imported from SVN: r1533]]

rbegin -> beforeEnd
rend   -> beforeBegin

[[Imported from SVN: r1414]]

*sigh*

[[Imported from SVN: r1410]]

[[Imported from SVN: r1404]]

[[Imported from SVN: r1333]]

[[Imported from SVN: r1319]]