canonicalize_file_name clashed with gnulib function. Additionally
it was declared in 2 places: emu/misc.h and util/misc.h. Added
grub_ prefix and removed second declaration.

	Fixes build for windows.

Add grub_util_disable_fd_syncs call to turn grub_util_fd_sync calls into
no-ops, and use it in programs that copy files but do not need to take
special care to sync writes (grub-mknetdir, grub-rescue,
grub-mkstandalone).

On my laptop, this reduces partmap_test's runtime from 1236 seconds to
204 seconds.

	the function of these files exceeds what can be sanely handled in shell
	in posix-comaptible way. Also writing it in C extends the functionality
	to non-UNIX-like OS and minimal environments.

	relpath.c from getroot.c as it's common between unix and haiku
	but otherwise haiku doesn't use any functions from unix getroot.c.

	New function.
	(grub_util_is_special_file): Likewise.

	open/read/write.

	fseeko.

	windows use unicode version.

	with AROS devs.
	* grub-core/osdep/aros/hostdisk.c: Likewise.

	moves OS-dependent parts from kern/emu/hostdisk.c to
	grub-core/osdep/*/hostdisk.c.