Add pre/post command signals to hook into operation of commands.
Merge branch 'master' of github.com:alexhayes/django-extensions

Conflicts:
	django_extensions/management/commands/update_permissions.py
Merge branch 'master' of https://github.com/django-extensions/django-extensions
Merge branch 'master' of https://github.com/django-extensions/django-extensions into feature/565-PrePostCommand
Fixes #565: Added better solution using decorator that wraps management commands to send signals for pre/post, documentation and tests.
Merge pull request #582 from alexhayes/feature/565-PrePostCommand

Feature/565 pre post command