decoder encounters certain kinds of messed up T.85 images.

squashing.

FS-4757 this should fix it but I am not happy with the way this is done but since polycom is one of the only phones that does this right I have no other choice

FS-2731 significantly reworked version of Emmanuel's patch to allow subscribing and notifying for the as-feature-event events.  we still need a module to handle the FS events for this automatically... coming soon to a repository near you

* Rename option ringback-during-collect to immediate-ringback
* Allow regular ringback tone with immediate-ringback, not just a wav file
* Do not request full frame of data, just packet_len which is what we receive per IO interval
* Ignore user data when playing ringback tone