config: Allow ConfBridge DTMF menus to have '#' as the first digit.

ConfBridge allows custom DTMF menus to be created in the confbridge.conf
file by assigning a DTMF key sequence to a sequence of actions as follows:

DTMF-sequence = action,action...

Unfortunately, the normal config file processing code interprets an
initial '#' character as starting a directive such as #include.

* Add the ability to escape the first non-blank character in a config line
so the '#' character can be used without triggering the directive
processing code.

(closes issue AFS-2)
(closes issue ASTERISK-22478)
Reported by: Nicolas Tanski
Patches:
      jira_asterisk_22478_v11.patch (license #5621) patch uploaded by rmudgett (modified)

Review: https://reviewboard.asterisk.org/r/2969/
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Merged revisions 402407 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 402416 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@402417 65c4cc65-6c06-0410-ace0-fbb531ad65f3