Have the method is_pkg_admin use a provided session

This fixes problem encountered when running the unit-tests using faitout
thus on postgresql where it was not using quite the same session to connect
to the database and was thus resulting in a SIGENV being sent to postgres
Adjust the calls to is_pkg_admin
Fix bug in unorphan_package

We only check if the user is a packager, not trying to unorphan a package
for someone else or part of the appropriate group if the user is not a pkgdb_admin
We do not care about the 'approveacls' ACL on orphaned packages.
Create a FAITOUT_URL variable allowing to easily switch the faitout server