enhanced permitopen matching (patch in bugzilla)

[Ryan]

I'd really like to get some feedback on the patch I posted to bugzilla about a 
month ago.

https://bugzilla.mindrot.org/show_bug.cgi?id=1513#c3

This patch adds support for CIDR ranges, wildcard matches, negated matches, 
port ranges and makes matches for ip addresses and hostnames work 
interchangeably.

This was done primarily by using already existing functions for from= in ssh 
keys.

I'm not very experienced with sockets or dynamic memory management so some 
more sets of eyes would be great.

-Ryan