Always install safe_asterisk; add configuration file support

This patch modifies the behavior of safe_asterisk in two ways:
(1) It modifies the Asterisk Makefile such that safe_asterisk is always
    installed on a 'make install'. This was done as bugfixes in the
    safe_asterisk script were not applied in previous version of Asterisk
    without first removing the old version of the script.
(2) In order to keep a newly installed version of safe_asterisk from impacting
    local modifications, a new config file - safe_asterisk.conf.sample - has
    been provided. Settings that were previously modified in safe_asterisk can
    be set there instead.

(closes issue ASTERISK-21965)
Reported by: Jeremy Kister
patches:
  safe_asterisk.patch uploaded by jkister (License 6232)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@394939 65c4cc65-6c06-0410-ace0-fbb531ad65f3