Add force option to dropdb

Hello,

I think adding a force option to dropdb is usefull for many purposes, mainly; scripting. For example, in a test enviroment, I restore a daily backup of production databases. The newly created databases are used as templates for development and also for reading, thus replacing them is completly safe.

I uses dropdb and pg_terminate_backend  for this purpose, since some users might forget to close connections.
I have had a look on dropdb.c and I have amended the code to also terminate client connections using pg_terminate_backend

So the functionallity of the dropdb if force option is used is as follows:
1. Terminate client connections using pg_terminate_backend
2. Drop the database

For the sake of completeness:
1. I think also, I need also to temporary disallow conecting to the database, is that right?
2. Is there other factors can hinder dropping database?

3. Should I write two patches one for pg_version>=9.2 and one for pg_version<9.2 

Regards