Add support for MSRP Alternative Connection Model

Ignore-this: 174b24474abbbcef7d348d2608be34f2

http://tools.ietf.org/html/draft-ietf-simple-msrp-acm-08

darcs-hash:20100615110404-56b4d-3b7f2b20cfd46af5221432c829eb2b93f9b67c0a
Disable MSRP ACM by default

Ignore-this: b35b957b21e9f33d03bfb5b657ba09ab

darcs-hash:20100616161202-56b4d-17590068315d6f04bceb69ac344957e34ef485eb