Remove libgettex3 from the 10.7 bootstrap tree.
It is no longer essential, and nothing in the main 10.7 tree depends on it.
Replace _min_fink_version with _require_dep, allowing arbitrary pkgnames

See comment-block for usage of this new function. Not bothering to
keep _min_fink_version as a legacy compat wrapper around it because
it's always been a private function (all uses here have been updated).