HEADS UP: bugs in GHC 6.12.2

[Simon Marlow]

Hi folks,

I'm sorry to say that in GHC 6.12.2, as a result of fixing a couple of 
bugs in 6.12.1, we (well, I) managed to introduce some more serious ones:

http://hackage.haskell.org/trac/ghc/ticket/4038
http://hackage.haskell.org/trac/ghc/ticket/4041

The first causes gtk2hs programs to crash, and we have a report of it 
affecting hmatrix too.  There's no workaround unfortunately: the problem 
is that we changed some data structures related to FFI calls, with the 
result that a nested callback (calling out to C, back to Haskell, out to 
C again and back to Haskell in the same thread) can result in a crash or 
a bogus result.

The second causes lazy bytestring's hGetContents to block waiting for a 
full buffer, when it should just return the data already read.  You can 
work around this by using bytestring-0.9.1.5 instead of the supplied 
0.9.1.6.

We'll put out 6.12.3 with fixes for these as soon as possible.  In the 
meantime, if you are still on 6.12.1 and not encountering any problems, 
I don't recommend upgrading.

Sorry for the inconvenience.

Cheers,
	Simon