* image.c: Fix minor problems reported by GCC 4.6.0.

* image.c: Fix minor problems reported by GCC 4.6.0.

(gif_load, svg_load_image): Rename locals to avoid shadowing.
(imagemagick_load_image): Fix pointer signedness problem by changing
last arg from unsigned char * to char *.  All uses changed.
Also, fix a local for similar reasons.
Remove unused locals.  Remove locals to avoid shadowing.
(fn_rsvg_handle_free): Remove; unused.
(svg_load, svg_load_image): Fix pointer signedness problem.