Allow "manage.py shell" to use IPython if present

[hbtaylor@…]

I cribbed the following from TurboGears. Their tg-admin.py shell command tried to import IPython and falls back to code.interact() if IPython isn't present. I prefer IPython for several reasons. I know I can run it manually if I want to, but it isn't available via a nice, easy command!

A modification like the following to "run_shell" in django.core.management seems to work (not my original work - I grabbed it from TG):

def run_shell():
    "Runs a Python interactive interpreter. Tries to run IPython if it exists"
    try:
        import IPython
        shell = IPython.Shell.IPShell()
        shell.mainloop()
    except ImportError:
        import code
        code.interact()

[Adrian Holovaty]

(In [1930]) Fixed #1202 -- Changed 'manage.py shell' to use IPython if present. Also added '--plain' option, which overrides IPython to use the standard Python interactive prompt