Corrects these bugs :  * Could not retrieve movies from the cameras (got the image having    the same base name instead).  Same behaviour for movie thumbnails,  * After correction of problem 1, got movie thumbnails that do    not fit the JPEG format.  * After correction of problem 1 & 2, part of some movie thumbnails had a    very bad quality! The phenomenon was aleatory.
Corrects these bugs :
 * Could not retrieve movies from the cameras (got the image having
   the same base name instead).  Same behaviour for movie thumbnails,
 * After correction of problem 1, got movie thumbnails that do
   not fit the JPEG format.
 * After correction of problem 1 & 2, part of some movie thumbnails had a
   very bad quality! The phenomenon was aleatory.

Following corrections were made :
 * Rewrite the sierra_read_packet routine : now it downloads movie thumbnails
   correctly (third bug).
 * Correction in the sierra_capture routine to make it generic regarding name
   of the folder the captured image is stored in.
 * Move update_fs_for_folder and sierra_change_folder from sierra.c
   to here.
 * Plus various other changes to try to be consistent between the
   different routines (when do we need to retry, error codes).
   Still work to be done there.
 * Add gp_filesystem_delete_all at the beginning of update_fs_for_folder.
 * Start documenting routines.

Tests :
 * Stuff was tested with an Epson 3000z (both USB and serial link).


git-svn-id: 40dd595c6684d839db675001a64203a1457e7319@2030 67ed7778-7388-44ab-90cf-0a291f65f57c

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