Fixes to polymorphic:  * Wrap save code in a transaction to avoid situation where e.g. an    Event is created before a LearnEvent, and another thread tries to    downcast the Event  * Replace the __subclasses__ iteration code with the old content_type    stuff, with the tweak that we use get_for_id instead of a ForeignKey    dereference, thus using the contenttypes cache and avoiding spurious    SELECTs when downcasting
Fixes to polymorphic:
 * Wrap save code in a transaction to avoid situation where e.g. an
   Event is created before a LearnEvent, and another thread tries to
   downcast the Event
 * Replace the __subclasses__ iteration code with the old content_type
   stuff, with the tweak that we use get_for_id instead of a ForeignKey
   dereference, thus using the contenttypes cache and avoiding spurious
   SELECTs when downcasting

intel-hpdd/intel-manager-for-lustre,intel-hpdd/intel-manager-for-lustre,intel-hpdd/intel-manager-for-lustre