List files that are needed to build the library

This list will be picked up by the modules at a later commit.
Specify source files explicitly rather than with glob
Allow uppercase alternatives for package location vars
Fix bug with whitespace at end of env.var.
Don't add anything if no precompiled header is specified
Only regenerate config var file if actually changed
Remove make execution wrapper
Merge pull request #8 from rolk/008_cmakeupd

Update CMake scripts to commit f3b76ac8 from opm-core