Bring build system up to current trunk
CMakeCache is local to the build and should not be in VC
Don't install debug syms for a library that isn't there
Only include library if there is one
Module mode CMake probe for opm-material
Only make target if there is any source files

If there is no source files, we set a blank target to signal to the
other components of the build system that they shouldn't be looking
for a library.
Only include files from the source directory

We want files from the source directory, relative to the source tree,
not everything under the source tree relative to the source sub-dir!
Merge pull request #1 from rolk/001_cmake

Changes to build a library-less project with current build-system