move some dialog-only flags to proper variables, namely

move some dialog-only flags to proper variables, namely
SIP_NOVIDEO, SIP_DIALOG_ANSWEREDELSEWHERE, SIP_PAGE2_NOTEXT,
SIP_PAGE2_OUTGOING_CALL
These are seldom used so the diff is relatively small.

Note that 'OUTGOING_CALL' is dangerously similar to another
dialog flag, 'SIP_OUTGOING', so the description will need to
clarify the different meaning of the two.

Also note that the description of NOTEXT is a bit unclear - does
it mean we don't support it, or 'not requested or not supported' ?

On passing fix a comment referring to video instead of text.

Finally, mark with XXX a possibly misleading debugging message.
(maybe the latter is worth backporting).

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@77739 65c4cc65-6c06-0410-ace0-fbb531ad65f3