This fixes bug #22663 ("25.0.91; python.el electric-indent misbehaviour
with 'except:'"). Note that the bug is not restricted to "except:" but
affects all statements that are dedented by an electric colon.

For instance, entering a colon after "else" in

    if do:
        something()
        else
    outside

results in

    if do:
        something()
    else:
        outside

before the bug fix but

    if do:
        something()
    else:
    outside

after the bug fix.

-- Joel