dsp.c: Fix multiple issues when no-interdigit delay is present, and fast DTMF 50ms...

dsp.c: Fix multiple issues when no-interdigit delay is present, and fast DTMF 50ms/50ms

Revert DTMF hit/miss detector to original -r349249 method with some changes, remove unnecessary;
  1. reseting of hits=0, when no signal, only need to set it once.
  2. incrementing of hits, when the hit is the same as the current hit.
  3. setting of lasthit, when it's the same as before.

Change HITS_TO_BEGIN to 2, MISSES_TO_END to 3

& 3 spelling mistakes

(closes issue ASTERISK-19610)
alecdavis (license 585)
Reported by: Jean-Philippe Lord
Tested by: alecdavis

Review: https://reviewboard.asterisk.org/r/2085/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@372239 65c4cc65-6c06-0410-ace0-fbb531ad65f3