Cleaned up error reporting in the image caches. Draw callbacks now throw rxml errors, and they get reported in a decent way in the image cache filesystem as well. This should finally avoid noisy pike backtraces for invalid cimg images etc. Rev: server/base_server/roxen.pike:1.1118 Rev: server/etc/modules/LazyImage.pmod/module.pmod:1.27 Rev: server/modules/graphics/cimg.pike:1.92 Rev: server/modules/graphics/gbutton.pike:1.127 Rev: server/modules/graphics/graphic_text.pike:1.316