Added log rollback functionality to LogDisplay.

Fixed a bug in ActorTalents:useTalent to correctly return the results of the talent action, activate, or deactivate code instead of the coroutine (co_wrapper) result (which normally always returns true).
The return value now correctly reflects talent success or failure, allowing AIs to try other actions when the talent code aborts.  (Not addressed in this commit.)
useTalent will automatically rollback log messages from aborted talents.  (i.e. no more "Monster rushes out!" spam when the Rush talent is attempted inside of minimum range)
Fixed a bug that was allowing NPC's to bump attack without enough energy.
Added some on_pre_use functions to staff-combat talents.