Add support for sip proxy-auth (407)
disable 100rel as it causes segfault/asserts in sofia-sip
Merge pull request #122 from mingewang/sip

support proxy_auth 407 and disable 100rel in sip module
session pointer not set to NULL after free in videoroom session free function, corrected it
Merge pull request #123 from Computician/master

setting pointer to NULL to match other plugins