Upgrade Skytools to version 3.0.3.
Change the `satisfied?` section of the Postgresql requirement to
look for `postgres` not `pg_config` because the build fails when
it can't find the former and because the system Postgresql has the
latter binary causing the Requirement to be met while the build
would fail. Tested using llvm and clang from XCode-4.3.2.
Signed-off-by: Adam Vandenberg <flangy@gmail.com>
