Remove hidden import

This should fix #5 (closed) nicely. Thanks to @duncanmmacleod to the pointer to __future__ import absolute_import we can achieve the desired behaviour. This has the added benefit that import glue.lal won't fail if lal is not installed (which it currently does). Calling glue.lal.CacheEntry will fail if lal is not installed, but that is the correct behaviour.

Of course the offending code, which is listed as deprecatedm could just be removed, but there exist even in glue a number of pointers to this.