Bring sig_analog extraction more into alignment with orig-trunk/v1.6.2 chan_dahdi.

Bring sig_analog extraction more into alignment with orig-trunk/v1.6.2 chan_dahdi.

* Restore SMDI support.
* Fixed initial value of struct analog_pvt.use_callerid.  It may get
forced on depending upon other config options.
* Call analog_dnd() instead of manual inlined code.
* Removed unused struct analog_pvt.usedistinctiveringdetection.
* Removed the struct analog_pvt.unknown_alarm flag.  It was really the
struct analog_pvt.inalarm flag.
* Use ast_debug() instead of ast_log(LOG_DEBUG).
* Rename several function's index variable to idx.
* Some formatting tweaks.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@295516 65c4cc65-6c06-0410-ace0-fbb531ad65f3