* grub-core/kern/misc.c (grub_strcmp): Use unsigned comparison as

	* grub-core/kern/misc.c (grub_strcmp): Use unsigned comparison as
	per common usage and preffered in several parts of code.
	(grub_memcmp): Likewise.
	(grub_strncmp): Likewise.
	* include/grub/misc.h (grub_strcasecmp): Likewise.
	(grub_strncasecmp): Likewise.
	* Makefile.util.def (cmp_test): New test.
	(grub_script_strcmp): Likewise.
	* tests/cmp_unit_test.c: New file.
	* tests/grub_script_strcmp.in: Likewise.
	* grub-core/fs/hfsplus.c (grub_hfsplus_cmp_catkey): Add a comment.