added note for user that the error msg from _set_error may be unrelated to real error
added note for user that the error msg from _set_error may be unrelated to real error


git-svn-id: 40dd595c6684d839db675001a64203a1457e7319@2899 67ed7778-7388-44ab-90cf-0a291f65f57c

gphoto/libgphoto2.OLDMIGRATION,gphoto/libgphoto2.OLDMIGRATION,gphoto/libgphoto2.OLDMIGRATION,gphoto/libgphoto2.OLDMIGRATION