Fixed SendMessage stripping extension from To: header in SIP MESSAGE

When using the MessageSend application to send a SIP MESSAGE to a non-peer,
chan_sip attempted to validate the hostname or IP Address.  In the process,
it stripped off the extension and failed to add it back to the sip_pvt
structure before transmitting.  This patch adds the full URI passed in
from the message core to the sip_pvt structure.

(closes issue ASTERISK-18903)
Reported by: Shaun Clark
Tested by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/1597/
........

Merged revisions 346040 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@346053 65c4cc65-6c06-0410-ace0-fbb531ad65f3