Switch gifsicle from archived giflossy fork to mainline - #473

pornel/giflossy has been archived since its --lossy support was merged
upstream. Mainline gifsicle carries it (src/gifsicle.c registers "lossy"
and handles LOSSY_OPT), so the fork is no longer needed.

Points the submodule at kohler/gifsicle and pins release v1.96 instead of
an untagged fork commit.

The ImageOptim patch is regenerated against v1.96: the old 1.89 patch no
longer applied, because mainline dropped the kc_set_gamma call from
do_colormap_change and added an argument to colormap_stream. The new
patch strips the same features and applies with no fuzz or offsets.

Renames the lossy pass from "Giflossy" to "Gifsicle lossy" in the UI,
since the fork is no longer what runs.

Mainline gifsicle split the k-d tree and colour-histogram code (kd3_*,
kchist_*) out of quantize.c into src/kcolor.c. quantize.c and xform.c
still call into it, so without kcolor.c the target compiles but fails
to link on ten undefined symbols.

The Xcode target compiles with HAVE_CONFIG_H and picks up the checked-in
gifsicle/config.h, which still described the archived fork: gifsicle
--version printed 1.88 for a 1.96 build, and the package metadata pointed
at pornel/giflossy. The version fields now match mainline's
AC_INIT([gifsicle],[1.96]), which sets no bug-report address or home page.

scripts/fetch-submodule also gains a submodule sync: git keeps a
submodule's original URL in .git/config once it is initialized, so an
existing checkout would keep fetching giflossy and then fail to apply the
1.96 patch against the stale 1.89 tree. The sync is best effort because
pngquant passes a nested path, which only the recursive update handles.

git submodule sync without --recursive only rewrites .git/config for the
superproject's own submodules, so a submodule of a submodule kept fetching
its old URL: the update below clones a nested submodule but never resyncs
one that already exists. pngquant/src/lib is exactly that case.

The path stays unquoted-safe now, and the failure remains suppressed on
purpose: a caller that passes a nested path (pngquant/Makefile asks for
src/lib) makes sync error out with "pathspec did not match", since that
path is no submodule of this repo. Only the recursive update can fetch it,
so aborting on a sync failure would break that caller.