Tweak MUMPS parameter via PETSc to avoid memory error in LU factorisation.
Fix build error.
Fixes for latest Xcode.
Fix namespace ambiguity in XML test.
Merge remote-tracking branch 'origin/garth/clang-fixes' into garth/mumps-parameter-for-bcs-demo
Demo fix for when PETSc is not installed.
Fix MPI namespave ambiguity.
Fix detection of compatible Python interpreter and library.
Add 'bool dolfin::has_petsc()' function.
Merge branch 'garth/fix-petsc-mumps-option'
Merge branch 'garth/mumps-parameter-for-bcs-demo'