- Add reget_buffer() function to AVCodecContext

- Add default reget_buffer implementation in libavcodec/utils.c
- Remove AVCodecContext.cr_available, no longer needed
- Remove CODEC_CAP_CR, no longer used
- Add img_copy() prototype to avcodec.h (function from imgconvert.c)
- Rename img_copy() to jpeg_img_copy() in libavformat/jpeg.c to avoid
conflict
- Updated msrle, msvideo1, rpza, smc to use reget_buffer

Originally committed as revision 2531 to svn://svn.ffmpeg.org/ffmpeg/trunk