Address #3310
- Rename BlockedOnDeadMVar -> BlockedIndefinitelyOnMVar
- Rename BlockedIndefinitely -> BlockedIndefinitelyOnSTM
- instance Show BlockedIndefinitelyOnMVar is now
"blocked indefinitely in an MVar operation"
- instance Show BlockedIndefinitelyOnSTM is now
"blocked indefinitely in an STM transaction"
clients using Control.OldException will be unaffected (the new
exceptions are mapped to the old names). However, for base4-compat
we'll need to make a version of catch/try that does a similar
mapping.