EXIF fixes by reald (closes #80)

commit 9c8226a1
Merge: e4483e5e 132ecc0f
Author: Dennis Real <github@tildepipe.org>
Date:   Sun Feb 5 17:24:17 2012 +0100

    Merge branch 'master' of ssh://github.com/reald/feh

commit e4483e5e
Author: Dennis Real <github@tildepipe.org>
Date:   Sun Feb 5 16:56:29 2012 +0100

    - improved handling of images which have exif tags but not ours
    - fixed uninitialized pointer in thumbnail mode
    - added nikon lens info if available

commit 132ecc0f
Author: Dennis Real <github@tildepipe.org>
Date:   Sun Feb 5 16:56:29 2012 +0100

    - improved handling of images which have exif tags but not ours
    - fixed uninitialzed pointer in thumbnail mode
    - added nikon lens info if available