SIP uri parsing cleanup

Now, the scheme passed to parse_uri can either be a
single scheme, or a list of schemes ',' delimited.
This gets rid of the whole problem of having to create
two buffers and calling parse_uri twice to check for
separate schemes.

Review: https://reviewboard.asterisk.org/r/343/



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@215522 65c4cc65-6c06-0410-ace0-fbb531ad65f3