Derive Typeable and Eq instances for TMVar, TChan (and TArray)

[Bas van Dijk]

Hello,

I noticed the stm types TMVar and TChan don't have Typeable and Eq
instances while their MVar counterparts do have them. I propose to add
them:

http://hackage.haskell.org/trac/ghc/ticket/3973

The patch bundle included in the ticket also contains patches that add
these instances to TArray. However I'm not sure if it makes sense to
have an Eq instance for TArray so it's probably wise to have some
discussion on this.

regards,

Bas