tigefa4u projects Trac

Fix for #5956.

Real errors in trac-admin now fall through to the console. This changes
trac-admin's exit status to 1 for these cases. Updated unit tests accordingly.

Deprecate potentially confusing permission error message. Logs should be
used by administrators to fix permission problems.

use tuple in `datefmt.http_date` since it gets optimized to a `LOAD_CONST` instead of building the list

Testing: merge through r5978, except for r5962, from trunk.

Add the `vulnerability_tickets.py` sample security plugin to deny access to tickets with "security" or "vulnerability" in the `keywords` or `summary` fields.

Testing: CamelCase words in the dictionary are 'rare', but they cause spurious failures. Flatten them.

Testing: Do a basic test to create a new report. All tests PASS.

Testing: Merge through r5971 from trunk, except for r5962. All tests PASS.

Testing: merge r5963 from trunk; the #5930 regression test still fails.