Fixed lots of warnings.

Rev: src/modules/Image/blit.c:1.27
Rev: src/modules/Image/colortable.c:1.34
Rev: src/modules/Image/encodings/gif.c:1.25
Rev: src/modules/Image/encodings/pnm.c:1.11
Rev: src/modules/Image/font.c:1.26
Rev: src/modules/Image/image.c:1.76
Rev: src/modules/Image/matrix.c:1.14
Rev: src/modules/Image/polyfill.c:1.19
Rev: src/modules/Image/togif.c:1.30
Rev: src/modules/Image/x.c:1.18