some bugfixes for empty strings, and properites which have just the factory default, but no currentvalue (as seen on the D700)
some bugfixes for empty strings, and properites
which have just the factory default, but no currentvalue
(as seen on the D700)


git-svn-id: 40dd595c6684d839db675001a64203a1457e7319@11261 67ed7778-7388-44ab-90cf-0a291f65f57c

msmeissn/libgphoto2,thusoy/libgphoto2,jbreeden/libgphoto2,gphoto/libgphoto2,msmeissn/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,jbreeden/libgphoto2,gphoto/libgphoto2,jbreeden/libgphoto2,jbreeden/libgphoto2,msmeissn/libgphoto2,gphoto/libgphoto2,thusoy/libgphoto2,thusoy/libgphoto2,thusoy/libgphoto2,jbreeden/libgphoto2,thusoy/libgphoto2,gphoto/libgphoto2,msmeissn/libgphoto2,msmeissn/libgphoto2