add a cmake test to check if the used file system is case sensitive

And fix the unit test for INCLUDE. This should make the test pass on
case insensitive file systems like the one of MacOS X. (Who uses that
anyway? ;))
Removed extra "," from WELTARG
Merge pull request #192 from andlaus/check_filesystem_case_sensitiveness

add a cmake test to check if the used file system is case sensitive