Don't probe for umfpack with cholmod unless latter is found
Include standard math runtime library when linking numerics
Add direct dependency on dune-common

We need to link to the library provided by dune-common, but dune-istl
does not pull this one in transitively.
Enable CMake < 2.8.5 clients to report Git version
Allow subdir builds with dunecontrol

dunecontrol will check for a dune.module file to regard the directory
as containing the module. If we put this is a sub-dir of the source,
it will get confused, so we shouldn't. There shouldn't be any
conflicting use-cases, as one cannot have several modules in the sub-
directory of one source (!?).
Merge pull request #192 from rolk/192_findlibs

Probe for indirect library dependencies