INVITE comformance issues

[vodik]

Related to #123, seems like there are a few issues with invites now. Making a super issue to track everything:

• 100 response are incorrectly tagged.
• 100 should not be forwarded by proxies.
• 100 is a special status code. Other unknown 1XX messages should be handled the same as a 183.
• ACK seems to be broken currently for INVITEs
• Can't easily catch other leg closing the INVITE (BYE or CANCEL)
• recv/iterator can hang indefinately in some cases

[vodik]

@ovv I'm just going to bite the bullet and rewrite/cleanup the dialog and transaction module. There is far too much technical debt int there - I couldn't find a quick fix.

[ovv]

@vodik Good idea. If possible having a common class for Dialog and DialogRequest (if we decide to go #119 way) would be nice.

If you are re-working that I'll leave those parts alone. I plan to work a bit on the Auth since I would like to support qop.

[vodik]

Go for it. And for what its worth, we're also testing ursine internally as well and it seems really promising as well.