extend mesh-compatibility check in Form::mesh() by marker meshes
Add function to get dofs associated with a (sub)space.
Add range argument for field split code.
Some dummy code for fieldsplits in pc.
Work on field split preconditioner.
Speed-ups and improvements related to field split.
Merge branch 'master' into fix-issue-88
Extract form mesh from markers before coefficients are investigated
Remove some loop edges in some graph builders.
Start adding PETSc error checking.
Add checks of PETSc return code in PETScLUSolver.
More PETSc error code checking.
Fix some PETSc error checks.
Merge branch 'master' into garth/check-petsc-return-code

Conflicts:
	dolfin/la/PETScLinearOperator.cpp
	dolfin/la/PETScMatrix.cpp
Add error code checking to PETScVector.
More PETSc error checking.
Fix declaration typo.
Prefer SuperLU_dist over MUMPS in PETSc interface. MUMPS via PETSc has been unreliable.
Apply SLEPx 3.4 fix.
Revert PETSc LU solver change and do not run Poisson-on-sphere demo in parallel