[Merge][Feature] -r1738:1749 Added generailzed PCG.

Original messages are:

> r1749 | mblatt | 2012-12-18 16:41:13 +0100 (Di, 18. Dez 2012) | 2 Zeilen
> Geänderte Pfade:
>    M /trunk/dune/istl/solvers.hh
> 
> use new name in message.
> 
> ------------------------------------------------------------------------
> r1748 | mblatt | 2012-12-18 16:40:38 +0100 (Di, 18. Dez 2012) | 2 Zeilen
> Geänderte Pfade:
>    M /trunk/dune/istl/solvers.hh
> 
> Bugfix: Removed Segfault.
> 
> ------------------------------------------------------------------------
> r1747 | mblatt | 2012-12-18 15:29:07 +0100 (Di, 18. Dez 2012) | 6 Zeilen
> Geänderte Pfade:
>    M /trunk/dune/istl/solvers.hh
> 
> Fixing overwrite of r1739 by r1740.
> 
> Shouldn't subversion prevent such a thing? I even could
> not use svn merge to restall the changes of r1739. 
> Really weired.
> 
> ------------------------------------------------------------------------
> r1743 | mblatt | 2012-12-18 11:22:24 +0100 (Di, 18. Dez 2012) | 2 Zeilen
> Geänderte Pfade:
>    M /trunk/dune/istl/solvers.hh
> 
> Use end and do not allow more steps than maxsteps.
> 
> ------------------------------------------------------------------------
> r1742 | mblatt | 2012-12-18 11:21:53 +0100 (Di, 18. Dez 2012) | 2 Zeilen
> Geänderte Pfade:
>    M /trunk/dune/istl/paamg/test/kamgtest.cc
> 
> Use default Krylov cycle.
> 
> ------------------------------------------------------------------------
> r1741 | mblatt | 2012-12-18 11:21:30 +0100 (Di, 18. Dez 2012) | 2 Zeilen
> Geänderte Pfade:
>    M /trunk/dune/istl/paamg/kamg.hh
> 
> Use the generalized PCG.
> 
> ------------------------------------------------------------------------
> r1740 | mblatt | 2012-12-18 11:13:11 +0100 (Di, 18. Dez 2012) | 5 Zeilen
> Geänderte Pfade:
>    M /trunk/dune/istl/paamg/test/amgtest.cc
>    M /trunk/dune/istl/solvers.hh
> 
> Added a generalized PCG solver
> 
> This solver allows the preconditioner
> to between iterations or even be nonlinear.
> 
> ------------------------------------------------------------------------
> r1739 | peter | 2012-12-18 10:58:21 +0100 (Di, 18. Dez 2012) | 1 Zeile
> Geänderte Pfade:
>    M /trunk/dune/istl/solvers.hh
> 
> output of argument w does not work


[[Imported from SVN: r1880]]