Don't use readlink to get dirname of install dir

If you use the path to the install directory (which seems the "normal" way of
doing things) then the readlink will return nothing and dirname will fail...

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Merge pull request #19 from dirkhh/fix-readlink

Don't use readlink to get dirname of install dir