dropdb --force

Hi,

I propose a simple patch (works-for-me), which adds --force (-f)
option to dropdb utility.

Pros:  This seems to be a desired option for many sysadmins, as this
thread proves: https://dba.stackexchange.com/questions/11893/force-drop-db-while-others-may-be-connected
Cons: another possible foot-gun for the unwary.

Obviously this patch needs some more work (see TODO note inside).

Please share opinions if this makes sense at all, and has any chance
going upstream.

The regression tests is simplistic, please help with an example of
multi-session test so I can follow.


Thanks,
Filip