Make blscfg module compatible at least up to the Fedora 19 GRUB core
The blscfg module isn't compatible with the GRUB core.img installed by any
release older than Fedora 21.
This is because the blscfg module calls to the grub_file_size() function to
check if the BLS file size is correct, but the struct grub_file used as the
parameter for this function changed in the GRUB version used in Fedora 21.
So the function returns a wrong file size due the .size field offset being
different in the older GRUB from Fedora 20 and earlier.
This is causing all the BLS files to be ignored due having a wrong size and
leading to GRUB menu not being populated on boot.
Signed-off-by: Javier Martinez Canillas <firstname.lastname@example.org>