Log Message:
Update to stm-2.5.0.0

2.5.0.0 Sep 2018
* Removed alwaysSucceeds and always, GHC's invariant checking
  primitives. (GHC #14324)
* Add lengthTBQueue to Control.Concurrent.STM.TBQueue (gh-9)
* Add stateTVar :: TVar s -> (s -> (a, s)) -> STM a combinator (gh-14)
* Switched newTBQueue and newTBQueueIO to accept Natural as size
  (gh-17)
* Switched signalTSemN and newTSem to accept Natural and Integer
  respectively (gh-17)

2.4.5.1 Sep 2018
* Fix incorrect bookkeeping of write capacity in flushTBQueue (gh-9)
* Avoid redundant writeTVars in flushTQueue to avoid unncessarily
  invalidating other transactions (gh-6)

2.4.5.0 Feb 2018
* Fix space leak in TBQueue (gh-2, GHC#14494)
* Make signalTSem resilient against Int overflows (gh-4)
* Make definition of readTQueue consistent with readTBQueue (gh-3,
  GHC#9539)
* Add flushTQueue to Control.Concurrent.STM.TQueue (gh-1)
* Add flushTBQueue to Control.Concurrent.STM.TBQueue (gh-1)
* Add signalTSemN operation (gh-5)

2.4.4.1 Dec 2015
* Add support for base-4.9.0.0
* Drop support for GHC 6.12 / base-4.2

2.4.4 Dec 2014
* Add support for base-4.8.0.0
* Tighten Safe Haskell bounds
* Add mkWeakTMVar to Control.Concurrent.STM.TMVar
* Add @since-annotations