When trying to perform enabled=yes followed by enabled=no
against FreeBSD the module would die with the following error:
TypeError: sub() takes at most 4 arguments (5 given)

The target FreeBSD client (8.2) is running python 2.6.6. It seems the
extra 'flags' argument was added to re.sub() in 2.7.

In fixing this issue I have attempted to create a general atomic method
for modifying a rc.conf file. Hopefully this will make it easier to add
other rc based platorms. The strip/split magic was inspired by the user
module.