Fixed a few warnings.

Rev: src/modules/Image/blit.c:1.46
Rev: src/modules/Image/colortable.c:1.90
Rev: src/modules/Image/colortable.h:1.22
Rev: src/modules/Image/colortable_lookup.h:1.12
Rev: src/modules/Image/encodings/gif.c:1.56
Rev: src/modules/Image/encodings/iff.c:1.8
Rev: src/modules/Image/encodings/ilbm.c:1.18
Rev: src/modules/Image/encodings/png.c:1.37
Rev: src/modules/Image/encodings/psd.c:1.22
Rev: src/modules/Image/encodings/ras.c:1.10
Rev: src/modules/Image/encodings/x.c:1.30
Rev: src/modules/Image/font.c:1.62
Rev: src/modules/Image/matrix.c:1.28
Rev: src/modules/Image/pattern.c:1.22