Don't print existing Content-Length header if adding a new one
Merge branch 'master' of github.com:Metaswitch/pjsip-upstream into extra_clen_hdr
Code review feedback
Add similar handling for Content-Type header
Merge pull request #27 from Metaswitch/extra_clen_hdr

[Reviewer Matt] Don't print existing Content-Length header if adding a new one