Trim same amount from strings before comparing

If you specified options in an environment variable containing a blank
at the end, then this would not compare equal to the other candidate,
which was stripped, causing the first added argument to drop out! This
is usually the flag for C++11 compliance, causing binary incompatibility
Merge pull request #170 from rolk/170_trimopts

Fix mysterious dropping of flags when specifying CXXFLAGS env.var.
Do not duplicate handling of duplicate libraries

There were (at least) three implementations of the same macro; these
have been collected into a separate helper module. (Note that this
means that FindERT is now not completely stand-alone anymore).
Separate inclusion of OpenMP library into reusable module

Other projects (which does not have a direct dependency on ERT) require
OpenMP; we desire to reuse this functionality into those projects.
Propagate information about whether module was found quietly
Merge pull request #171 from rolk/171_openmp

Refactor OpenMP support to be reusable