Fix extension matching with the '-' char.

The '-' char is supposed to be ignored by the dialplan extension matching.
Unfortunately, it's treatment is not handled consistently throughout the
extension matching code.

* Made the old exten matching code consistently ignore '-' chars.

* Made the old exten matching code consistently handle case in the
matching.

* Made ignore empty character sets.

* Fixed ast_extension_cmp() to return -1, 0, or 1 as documented.  The only
user of it in pbx_lua.c was testing for -1.  It was originally returning
the strcmp() value for less than which is not usually going to be -1.

* Fix character set sorting if the sets have the same number of characters
and start with the same character.  Character set [0-9] now sorts before
[02-9a] as originally intended.

* Updated some extension label and priority already in use warnings to
also indicate if the extension is aliased.

(closes issue ASTERISK-19205)
Reported by: Philippe Lindheimer, Birger "WIMPy" Harzenetter
Tested by: rmudgett

Review: https://reviewboard.asterisk.org/r/2201/
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Merged revisions 376688 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 376689 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 376690 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@376691 65c4cc65-6c06-0410-ace0-fbb531ad65f3