Trunk 1.8

Unfortunately, this branch has started long time ago in svn repository. And even worse it contains work 
from two other branches started nearly three years ago. So it contains several functionalities mixed together.

Pull request contents:
- updates in FindPETSc = synchronisation with Jed Brown's version
- FindBDDCML, InstallBDDCML, InstallBLOPEX 
  ... and other changes in CMake/Modules ... all provides automatic installation of BDDCML in CMake
- changes in main CMakeList, makefile, ... just incorporate BDDCML
- Major changes in LinSys class and its descendants (LinSys_PETSC, LinSys_BDDC)
  removed solve.*
 this involves some changes here and there, namely usage of Distribution class.
- SchurComplement can detect block-diagonal structure of eliminated block and compute its inverse
- in fields use Space<spacedim>::Point instead of Point macro (clash with MUMPS)
- minor fix in src/input