Module mode CMake probe for opm-material
Upgrade Findopm-material to use separate prerequisite list

This will now be included both by the find module and by the project
file itself.
Merge pull request #311 from rolk/311_material

Find module for opm-material
Merge remote-tracking branch 'upstream/master'
Allow PCH option to be on even if there is no library
Only build before library target if there is any
Only configure libtool for libraries that exist
Merge pull request #312 from rolk/312_nolib

Allow several options to be used even if we don't have a library
Merge remote-tracking branch 'upstream/master'