[PATCH] [cmake] Makes arbitrary build subdirectories possible.

Instead of guessing the suffix or subdir of the build directory,
we now simply compare PROJECT_{BINARY,SOURCE]_DIR to detect it.
By this e.g. opm-core/opm-parallel is a possible build directory, too.
[cmake] Makes arbitrary build subdirectories possible for opm-parser.
Merge pull request #88 from blattms/arbitrary-build-dir-support

Arbitrary build directory support for opm-parser and cjson