Fax gateway functionality (i.e. translating between a T.30 terminal and a T.38

terminal). Can be enabled on a channel by setting FAXOPT(gateway)=yes in the
dialplan.

Big thanks to irroot for porting this code to use the framehooks api.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@325816 65c4cc65-6c06-0410-ace0-fbb531ad65f3