setup.hint requires error in expat package

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

I don't know why upset didn't catch this but expat apparently relies on
a nonexistent package:

    requires: cygwin libexpat1 libexpat-devel
                               ^^^^^^^^^^^^^^

I've changed that to libexpat1-devel.

Warren, please make a note of this and make sure it is changed in your
copy too.  Either that or let me know if there is something else that
needs to be done.

cgf