Fix 'eups distrib install' breakage caused by 119236b

Commit 119236b stopped exporting setup() and unsetup() functions, breaking 'eups distrib install'.  We now source setups.sh at the beginning of eupspkg-generated build script to make sure the EUPS environment is correctly set up.

The motivation for the change was posix compliance (especially in light of the shellshock exploit), so reverting the eups changes is not appropriate.