gnupload: we hold the master copy of this script now

gnupload: we hold the master copy of this script now

For motivation and more information, see:
<http://lists.gnu.org/archive/html/bug-gnulib/2012-01/msg00222.html>

* build-aux/gnupload: Make it clear in the heading comments that the
master copy of this file is maintained by gnulib.  Since we are at
it, bump its copyright year and ...
($scriptversion): ... the date in its version.
($usage): Patches and bug reports should be sent to the gnulib list,
not the automake one.
* config/srclist.txt: Don't try to sync 'gnupload' from automake
anymore.