Change D-channel warning to be less confusing on non-NFAS setups.

The "No D-channels available!  Using Primary channel as D-channel anyway!"
WARNING message has been confusing on non-NFAS setups.  The message refers
to things that are NFAS specific.

* Changed the warning to several different warnings to be more accurate
for the situation and less confusing as a result:
"No D-channels up!  Switching selected D-channel from X to Y.",
"No D-channels up!", and
"D-channel is down!".
........

Merged revisions 342484 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 342485 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@342486 65c4cc65-6c06-0410-ace0-fbb531ad65f3