Moved clean, brconfig, enable from debian into brg

The clean(), brconfig(), and enable() functions from the debian support
script can be useful for all client support scripts, so they have been
moved into brg itself.
Standardized on $brg_tmp for temp use/bootstrap

In order to make the clean function more flexible, it now removes
$brg_tmp rather than $output/brg-tmp . centos and debian scripts have
both been updated to use this variable elsewhere as well.
Error messages using stderr

Created error() function and updated brg itself to use that to display
errors.