Foreign.C.Error.Errno should be an instance of (Eq,Ord, Show... others?)

[TomMD]

Errno, the Haskell encapsulation of the CInt 'errno' value, should be an instance of the commonly used type classes so higher level data structures that include it aren't bothered.

This change will break code that has custom instances for Errno, but this should be little, if any, code.

[TomMD]

Pay no attention to the previous patch - this on actually compiles ;-)

[igloo]

Please use  http://www.haskell.org/haskellwiki/Library_submissions if you want to propose this.