Make the config parser remove escaping backslashes

Make the config parser remove escaping backslashes

The config parser in Asterisk does not currently remove a backslash that is
used to escape a semicolon which would otherwise be interpreted as the start
of a comment.

The change here causes that backslash to be removed, but does not create a
real escape system in the config parser.  The biggest complication with a real
escape system would be breaking existing configs everywhere (parsing \\ as \
and breaking on escaped non-semicolon characters) even though it would be the
"right" way to do things.

(closes issue ASTERISK-17121)
Review: https://reviewboard.asterisk.org/r/1724/

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@354655 65c4cc65-6c06-0410-ace0-fbb531ad65f3