Amend Git update command to ensure already-initialized extensions are updated

See answer and comments at http://stackoverflow.com/a/10168693/513536
Merge pull request #2057 from DavidOliver/git-update-extensions

Amend Git update command to ensure already-initialized extensions are updated
Better check for development versions
Update jQuery to 2.1.1
Merge branch 'integration' of github.com:symphonycms/symphony-2 into integration
Release 2.4
Merge branch 'integration' into bundle