* configure.in: add check for libexif version >= 0.6.0,
necessary because of nasty incompatible api change.
* plug-ins/jpeg/exif-handling.txt: removed from here...
* devel-docs/exif-handling.txt: ...and added here
* plug-ins/jpeg/jpeg-exif.c
* plug-ins/jpeg/Makefile.am
* plug-ins/jpeg/jpeg-load.c
* plug-ins/jpeg/jpeg.c
* plug-ins/jpeg/jpeg.h: extract info from exif on loading,
and add info to exif on saving, addresses bug #56433,
bug #61499, and bug #121810.
William Skaggs