Fix Background within a Macro for FreePBX.

Fix Background within a Macro for FreePBX.
If the single digit DTMF is an extension in the specified context, then
go there and signal no DTMF.  Otherwise, we should exit with that DTMF.
If we're in Macro, we'll exit and seek that DTMF as the beginning of an
extension in the Macro's calling context.  If we're not in Macro, then
we'll simply seek that extension in the calling context.  Previously,
someone complained about the behavior as it related to the interior of a
Gosub routine, and the fix (#14011) inadvertently broke FreePBX
(#14940).  This change should fix both of these situations, but with the
possible incompatibility that if a single digit extension does not exist
(but a longer extension COULD have matched), it would have previously
gone immediately to the "i" extension, but will now need to wait for a
timeout.
(closes issue #14940)
 Reported by: p_lindheimer
 Patches:
       20090420__bug14940.diff.txt uploaded by tilghman (license 14)
 Tested by: p_lindheimer

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@193119 65c4cc65-6c06-0410-ace0-fbb531ad65f3