Added signal which is fired when server needs restart

As we all know, adding, removing or changing apphook pages requires a
server restart. Until now, the maintainer/content-editors of a site
had to do and detect this manually.

I propose we add a signal ``cms.signals.urls_need_reloading`` which
fires when the CMS detects the server needs a restart.

This signal is just sent by the django CMS. The core itself does nothing
when this signal is sent. However it allows developers to write custom
listeners to that signal that take an appropriate action in their
envirnment.

For some common use cases, there might even be generic implementations
(outside djagno-cms core) which solve this issue (eg killing os.getppid
in single-server gunicorn systems).
restored Python 2.5 compatibility
tests and migration fixes

* Made sure plugin migrations run after cms
* Added frozen cms to inherit migration
* Fixed namespace issues in tests
Update 0002_fieldchanges.py
consolidated all scripts into develop.py
Merge remote-tracking branch 'origin/develop' into develop
Merge branch 'develop' into tests-cleanup
Fixed a bug when the page had no .lft or .rght

I'm not suer whether page should always have a .lft and a .rght or not.
If not it's a clean fix. Otherwise, you'll need to investigate why/how the page object came with .lft and .rght == None.
Merge remote-tracking branch 'origin/develop' into tests-cleanup
Merge remote-tracking branch 'linova/patch-2' into tests-cleanup
fixed no_sekizai test failing isolated
Added docopt requirement, isolated parallel
Fixed request.current_page leaking
for_page now raises a useful error when MPTT attrs aren't set
update admin style
Merge remote-tracking branch 'origin/develop' into tests-cleanup
all tests pass in isolated mode now
Merge remote-tracking branch 'origin/develop' into tests-cleanup
Merge remote-tracking branch 'origin/develop' into tests-cleanup
Fixed last failing test