Ebuild for htcondor (fixes #81)

As discussed in issue #81, Condor has changed its name to HTCondor for legal reasons. It has also changed (since the last condor ebuild in portage) from an autotools build system to CMake. This pull request creates a new cmake-utils ebuild for HTCondor.

I had quite a bit of trouble getting all the files to install in the right place, but I think I have cracked it now. HTCondor requires quite a lot of post-install configuration but I think that can be left to the user rather than included in the ebuild.