patch applied (packages/directory): Fix doesDirectoryExist; fixes trac #1490

[Ian Lynagh]

Sat Jul 21 13:01:54 PDT 2007  Ian Lynagh <igloo at earth.li>
  * Fix doesDirectoryExist; fixes trac #1490
  We used to always strip trailing path separators from the path we were
  given, but mingw's stat succeeds for C:\ and C:\foo but fails for C:
  and C:\foo\. Thus we now use a trailing slash if and only if the path
  we are given is a drive.

    M ./System/Directory.hs -8 +2