The attached patch enables PostgreSQL CVS to build cleanly under Cygwin

The attached patch enables PostgreSQL CVS to build cleanly under Cygwin
when built against readline 4.2.  Specifically, it handles the deprecation
of

    filename_completion_function()

with preference for

    rl_filename_completion_function()

Although, I was motivated by Cygwin support, IMO this patch is appropriate
for all platforms.  To quote from the readline source:

    #if 0
    /* Backwards compatibility (compat.c).  These will go away sometime. */
    ...
    extern READLINE_EXPORT(char, *filename_completion_function) ...
    #endif

Note that this patch is modeled after the one by Peter Eisentraut for
completion_matches():

    http://www.ca.postgresql.org/~petere/readline42.html
I tested this patch under the following environments:

    Cygwin with readline 4.1
    Cygwin with readline 4.2
    Linux with readline 2.2.1
    Linux with readline 4.2

and it behaved as expected.

Jason Tishler