haskeline should also work with new mt-2.1.1

[Christian Maeder]

Hi,

trying to install haskeline together with other packages using 
cabal-install-0.14.0 resulted in a failure due to a too restrictive 
constraint.

 > cabal install mtl haskeline --dry-run
Resolving dependencies...
In order, the following would be installed (use -v for more details):
haskeline-0.4

# because mtl-2.1.1 is already installed

This installation of haskeline-0.4 fails!

 > cabal install transformers haskeline --dry-run
Resolving dependencies...
In order, the following would be installed (use -v for more details):
mtl-1.1.1.1
haskeline-0.6.4.6

# transformers-0.3.0.0 is already installed

 > cabal install haskeline --dry-run
Resolving dependencies...
In order, the following would be installed (use -v for more details):
transformers-0.2.2.0
mtl-2.0.1.0
haskeline-0.6.4.6

Cheers Christian