various db constraints allow trailing newlines

[Michael Hudson-Doyle]

There are several database constraints in trusted.sql that match a name against a regular expression ending in $, aiming to allow python-identifier like names.

However, $ allows for a trailing newline, so these constraints aren't doing what they intend (they should end with \Z).

The fix for bug #137237 fixed valid_name and valid_branch_name which were causing actual problems. I *think* the other constraints are reasonably safe because of schema constraints, so this is low-ish priority, but they should still be fixed.