Change the remove_on_pull flag on ast_bridge_hook to be a set of flags.

This change is used to make bridge hook removal more generic. This way,
depending on the circumstance, the appropriate bridge hooks may be
removed.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@390510 65c4cc65-6c06-0410-ace0-fbb531ad65f3