add test for optional select custom fields (see r3762)
Fixed another broken unit-test.
Fixed unit-test.
Sync the `UPGRADE` file and the TracUpgrade wiki page.
Add note about changed argument list for `trac-admin initenv`.
Preparing for release
Another follow-up to r3756: don't delete the connection pool at thread shutdown.
Follow-up to r3756: make the !ConnectionPool really thread-safe by tracking in the !PooledConnection instance the thread which created it. Should fix #3504.
fixes #3763 re broken support for optional ticket custom select fields
Remove debug output leftover from connection pool code.
