Add System.FilePath.Cygwin

[NeilMitchell]

I propose we add the module System.FilePath.Cygwin to the filepath library. This module would be based on System.FilePath.Windows but with '/' as the preferred path separator, rather than '\\' as for Windows. This module would never be available as System.FilePath, and would always have to be imported specifically if wanted.

The desire for this module comes from working with the Cygwin shell, which supports Windows syntax but requires the alternative separator. I have been using such a module for a few months, and find it very useful.

There are no backward compatibility concerns, as it is a new separate module.

Discussion deadline: 18th June 2009.

[NeilMitchell]

Some people thought it was a good idea. There was discussion of how to deal with drives, in particular support for /cygdrive/c/ etc. Simon Marlow suggested that perhaps System.FilePath?.POSIX might be more appropriate in most cases. Neil realised that while originally his FilePath?.Cygwin module had done before than POSIX, increasingly it was becoming more like POSIX.

Concensus was to reject this proposal, but if anyone comes up with a particular application thatn requires a distinction between Cygwin and POSIX style filepaths, then perhaps it could be reopenned.