maint: fix copyright dates that were munged by a maintenance script

maint: fix copyright dates that were munged by a maintenance script

* gunzip.in, gzexe.in, zcat.in, zcmp.in, zdiff.in, zforce.in:
* zgrep.in, zless.in, zmore.in, znew.in:
A script went awry when updating copyright dates in gzip's shell
scripts.  It should update comments to look like "# Copyright (C)
2007, 2010 Free Software Foundation, Inc." (with a set of years)
and version messages to look like "Copyright (C) 2010 Free
Software Foundation, Inc." (with just the most-recent year).
Instead, it sometimes ignored one, sometimes the other, and
typically put ranges into version messages.  Fix all this stuff by
hand, using dates that I divined from the change logs (so they're
a bit more accurate than script-generated dates).  We need to fix
the script before it runs in 2011.