cabal-install-1.18 on GHC-6.12

[Henning Thielemann]

On Mon, 28 Oct 2013, Johan Tibell wrote:

> This is my fault. I don't know if it's worth another Cabal release to 
> fix it though. 6.12 is more than 3 years old now.

I have three (remote) machines where I could compile and run my stuff, all 
of them have GHC-6.12.1 (Ubuntu 10.04 LTS). If mask_ can be easily 
replaced by something different, this would be nice.