Set ignore_user_abort for the duration of transactions and while locks are in place in an attempt to try and prevent problems with duplicate bookings being seen on sites running with persistent database connections (see SF Bugs 314).

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2886 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7