Use -install_name on MacOS X when the installation path is known

Kudos to yrmt@ for the hint
Code cleanup
Introduced a test suite for the configure project
No longer hardcode the target file
Added a test for libraries on MacOS X (Darwin)
Slightly improved the tests log
Implemented library versioning on MacOS X (needs more work)
Also test for proper library (un)installation (fails with MacOS X)
Registered the Darwin library test case as a known failure
Default to "$(CC) -dynamiclib" on MacOS X for $(CCSHARED)
Abstract a good part of the output in helpers
Added a test for plug-ins as well
Fixed "make install" on MacOS X
Fixed "make uninstall" on MacOS X
The "library" test now succeeds on MacOS X as well
Pass all the tests again
Re-generated the Makefiles
Fixed building with OBJDIR