This patch changes the install to only install the hook script if
DAHDI is enabled. It also adds the script to the uninstall task, and
moves the DAHDI_UDEV_HOOK_DIR variable so that it's not between the
_MAKEOPTS variables and their comment.

This allows installs which specify a --prefix to work normally, as
long as they don't enable DAHDI.

Review: https://reviewboard.asterisk.org/r/3972/
........

Merged revisions 423281 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@423283 65c4cc65-6c06-0410-ace0-fbb531ad65f3