Moved GIF {en,de}code to _Image_GIF.

Rev: src/modules/Image/acconfig.h:1.5
Rev: src/modules/Image/configure.in:1.16
Rev: src/modules/Image/encodings/Makefile.in:1.32
Rev: src/modules/Image/encodings/any.c:1.19
Rev: src/modules/Image/encodings/configure.in:1.6
Rev: src/modules/Image/encodings/encodings.h:1.2
Rev: src/modules/Image/encodings/gif.c:1.61(DEAD)
Rev: src/modules/Image/encodings/gif_lzw.c:1.10(DEAD)
Rev: src/modules/Image/encodings/gif_lzw.h:1.9(DEAD)
Rev: src/modules/Image/image.h:1.44
Rev: src/modules/Image/initstuff.h:1.10
Rev: src/modules/_Image_GIF/.cvsignore:1.1
Rev: src/modules/_Image_GIF/Makefile.in:1.1
Rev: src/modules/_Image_GIF/acconfig.h:1.1
Rev: src/modules/_Image_GIF/configure.in:1.1
Rev: src/modules/_Image_GIF/gif_lzw.c:1.1
Rev: src/modules/_Image_GIF/gif_lzw.h:1.1
Rev: src/modules/_Image_GIF/image_gif.c:1.1
Rev: src/modules/_Image_GIF/testsuite.in:1.1