Creation of a new branch to allow the book_ahead policies to split between the ability to create new bookings and the ability to edit or delete existing bookings.

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/branches/create_policy@2876 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
First version of the separation of book_ahead into create_ahead and delete_ahead, allowing policies to distinguish between creating new bookings and editing or deleting existing ones.   Still to do:  test PostgreSQL; adjust draggable bookings code to recognise bookings that can't be edited; and add messages when you try and delete a booking that can't be (at the moment the booking is just silently not deleted)

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/branches/create_policy@2877 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
Stopped MRBS sending an email when nothing has been deleted

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/branches/create_policy@2878 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
Fixed undefined variable problem

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/branches/create_policy@2879 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
Added checks for use of old book_ahead config variables and tidied up checks for previously discontinued config variables

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/branches/create_policy@2889 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
Merged in latest changes from the trunk

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/branches/create_policy@2890 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
Re-integrated the create_policy branch back into the trunk.   The book_ahead capabilities have been split into create_ahead and delete_ahead capabilities, allowing finer control of policies.  It is now possible to distinguish between creating new bookings and editing or deleting existing bookings.   (An edit requires a new booking to be created and the old one to be deleted).

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2891 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7