* util/update-grub_lib.in (convert_system_path_to_grub_path): Abort if
file doesn't exist, or if it is in a filesystem grub can't read.
* util/update-grub.in: Set fallback for GRUB_FS check to "unknown". Do
not abort if GRUB_DRIVE could not be defined. Rearrange generated
header comment to fit in 80 columns when the variables are resolved.
* util/grub.d/00_header.in: Only set root variable when GRUB_DRIVE
could be identified by update-grub. Remove redundant check for
unifont.pff existance (since convert_system_path_to_grub_path now
handles that).
* util/update-grub_lib.in: New file.
* DISTLIST: Add update-grub_lib.in.
* conf/common.rmk: Generate update-grub_lib and install it in
$(lib_DATA).
* Makefile.in: Add install routine for $(lib_DATA).
* util/grub.d/00_header.in: Use convert_system_path_to_grub_path()
function provided by update-grub_lib to support arbitrary paths of
unifont.pff.
* util/update-grub.in: Use convert_system_path_to_grub_path() to
initialize GRUB_DRIVE_BOOT and GRUB_DRIVE_BOOT_GRUB variables.
