return grub_usb_err_t for cosistency. All users updated.

	same kind.

	due to delayed attach.

	descriptor to just receive it as argument rather than endpoint
	address.

* include/grub/usb.h (grub_usb_iterate_hook_t): New type.
(grub_usb_controller_iterate_hook_t): Likewise.
(grub_usb_iterate): Add hook_data argument.
(grub_usb_controller_iterate): Likewise.
(struct grub_usb_controller_dev.iterate): Likewise.

Update all implementations and callers.

	compact and more efficient code.

	* grub-core/kern/list.c (grub_list_push): Moved from here ...
	* include/grub/list.h (grub_list_push): ... to here. Set prev.
	(grub_list_remove): Moved from here ...
	* include/grub/list.h (grub_list_remove): ... here. Use and set prev.
	(grub_prio_list_insert): Set prev.
	* include/grub/list.h (grub_list): Add prev. All users updated.

	* grub-core/bus/usb/usb.c (grub_usb_device_initialize): Fail if
	configcnt == 0.
	* include/grub/usb.h (grub_usb_err_t): New enum value
	GRUB_USB_ERR_BADDEVICE.

	needed by libusb wrapper.

	* disk/ata.c: Spelling fixes.
	* disk/raid.c: Likewise.
	* disk/usbms.c: Likewise.
	* disk/dmraid_nvidia.c: Likewise.
	* kern/ieee1275/openfw.c: Likewise.
	* kern/ieee1275/init.c: Likewise.
	* kern/ieee1275/cmain.c: Likewise.
	* boot/i386/pc/cdboot.S: Likewise.
	* video/readers/png.c: Likewise.
	* video/i386/pc/vbe.c: Likewise.
	* fs/udf.c: Likewise.
	* fs/hfs.c: Likewise.
	* fs/reiserfs.c: Likewise.
	* efiemu/runtime/efiemu.c: Likewise.
	* efiemu/main.c: Likewise.
	* efiemu/mm.c: Likewise.
	* include/grub/elf.h: Likewise.
	* include/grub/xnu.h: Likewise.
	* include/grub/usbdesc.h: Likewise.
	* include/grub/usb.h: Likewise.
	* include/grub/script_sh.h: Likewise.
	* include/grub/lib/LzmaEnc.h: Likewise.
	* include/grub/efiemu/efiemu.h: Likewise.
	* include/grub/command.h: Likewise.
	* normal/menu.c: Likewise.
	* normal/main.c: Likewise.
	* normal/datetime.c: Likewise.
	* bus/usb/uhci.c: Likewise.
	* mmap/i386/uppermem.c: Likewise.
	* mmap/mmap.c: Likewise.
	* commands/acpi.c: Likewise.
	* commands/test.c: Likewise.
	* partmap/apple.c: Likewise.
	* font/font.c: Likewise.
	* loader/sparc64/ieee1275/linux.c: Likewise.
	* loader/macho.c: Likewise.
	* loader/i386/bsd_trampoline.S: Likewise.
	* loader/i386/bsd.c: Likewise.
	* loader/xnu.c: Likewise.
	* term/i386/pc/vesafb.c: Likewise.
	* term/usb_keyboard.c: Likewise.
	* util/resolve.c: Likewise.
	* util/getroot.c: Likewise.

        * Makefile.in (enable_grub_emu_usb): New variable.
        * conf/i386-pc.rmk (grub_emu_SOURCES): Add `disk/scsi.c'.
        (grub_emu_SOURCES) [grub_emu_SOURCES]: Add `disk/usbms.c',
        `util/usb.c', `bus/usb/usb.c' and `commands/usbtest.c'.
        (grub_emu_LDFLAGS): Add `$(LIBUSB)'.
        (pkglib_MODULES): Add `usb.mod', `uhci.mod', `ohci.mod',
        `usbtest.mod' and `usbms.mod'.
        (usb_mod_SOURCES, usb_mod_CFLAGS, usb_mod_LDFLAGS)
        (usbtest_mod_SOURCES, usbtest_mod_CFLAGS, usbtest_mod_LDFLAGS)
        (uhci_mod_SOURCES, uhci_mod_CFLAGS, uhci_mod_LDFLAGS,
        (ohci_mod_SOURCES, ohci_mod_CFLAGS, ohci_mod_LDFLAGS)
        (usbms_mod_SOURCES, usbms_mod_CFLAGS, usbms_mod_LDFLAGS): New
        variables.

        * disk/usbms.c: New file.

        * include/grub/usb.h: Likewise.

        * include/grub/usbtrans.h: Likewise.

        * include/grub/usbdesc.h: Likewise.

        * bus/usb/usbtrans.c: Likewise.

        * bus/usb/ohci.c: Likewise.

        * bus/usb/uhci.c: Likewise.

        * bus/usb/usbhub.c: Likewise.

        * bus/usb/usb.c: Likewise.

        * commands/usbtest.c: Likewise.

        * util/usb.c: Likewise.

        * include/grub/err.h (grub_err_t): Add `GRUB_ERR_IO'.

        * configure.ac: Test for libusb presence.

        * util/grub-emu.c (main) [HAVE_LIBUSB_H]: Call `grub_libusb_init'.