Release Djblets 0.7.23.
Update print statements to use the new function syntax.

In python 3, print is a function rather than a statement. This is helpfully
included in python 2.6+ with a __future__ import.

Several of our print statements existed inside management commands. The proper
way to output inside of a command is with self.stdout.write (or
self.stderr.write), so I've updated all of those.

Testing done: Ran unit tests
Reviewed at https://reviews.reviewboard.org/r/4903/
Remove the blesscss compiler.

We've converted to requiring a local install of the less tool, and the blesscss
service isn't running anymore. This isn't necessary or useful anymore.
Replace 'has_key' with 'in'

There are several places (mostly to do with caches) where we use the old
has_key method. The idiomatic syntax for this is to use the 'in' operator.
Caches implement __contains__, so this works fine.

Testing done: Ran unit tests.
Remove ast_compat

Since we have a minimum of Python 2.6 for the next major version of djblets, we
can get rid of this compatibility mechanism.
Bump to 0.7.24 dev.
Merge branch 'release-0.7.x'
Fix breakages with the webapi unit tests.

These unit tests have been broken a little while, due to the old
mimetypes lists being removed. They've been fixed to test the new
variables.