tigefa4u projects Trac

Testing: twill will compile the regex for us, and will give a better failure message this way.

Testing: Merge through r5927 from trunk

Move the `open_environment` from `trac.web.main` to `trac.env`. This function is responsible for the thread-safe caching of environments, and automatically performing the check for needed upgrades, features which may be generally useful outside of the web frontend.

Cleaner way of creating `HTTPException` subclasses.

Add a first version of the Dutch translation.

Update all currently present locales with the regenerated pot.

Minor changes to ticket template to get rid of unnecessary usage of `py:attrs`.

Fix typo in ticket template. Closes #5875.

Update the pot.

Merge with revisions 5888-5892,5897,5899-5902,5904-5909,5912.