RFD: deprecate permissions-related stuff in System.Directory

[Malcolm Wallace]

Simon Marlow <simonmarhaskell at gmail.com> wrote some fairly convincing
arguments against the universal use of get/setPermissions:

> These functions are hardly ever used.
> 
> There are a few more uses of `getPermissions`, but as pointed out
> above,  these are usually flawed.  In any case they can usually be
> replaced by  openFile.

I have a perfectly OK use of getPermissions: in hmake, there is a
routine that scans the PATH variable looking for an executable with a
given name.  Basically, it is a Haskell implementation of the unix
'which' command.  There is no actual use of the executable, just a test
to report/reject the candidate pathname.

Regards,
    Malcolm