Add an 'X' option to the asterisk application which enables #exec for configuration files.

This option can be used to enable #exec support in the asterisk.conf configuration file.

(closes issue #16260)
Reported by: atis
Patches:
      exec_includes.patch uploaded by atis (license 242)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@232510 65c4cc65-6c06-0410-ace0-fbb531ad65f3