New scary warning in 1.7.0

[Christopher Faylor]

http://cygwin.com/ml/cygwin-cvs/2006-q3/msg00105.html

This adds this type of warning to cygwin:

c:\>ls c:/
cygwin warning:
  MS-DOS style path detected: c:/
  Preferred POSIX equivalent is: /c
  CYGWIN environment variable option "nodosfilewarning" turns off this warning.
  Consult the user's guide for more details about POSIX paths:
    http://cygwin.com/cygwin-ug-net/using.html#using-pathnames
  ...

Unless turned off with CYGWIN=nodosfilewarning, the above warning shows
up once per user/per cygwin invocation, i.e., there is a flag stored in
the users's shared memory region.

I'm not 100% sure that the benefit here will outweigh the outcry but
Corinna and I want to give it a try and see what happens.

cgf