Just "packed" doesn't always pack the way we expect.

        * 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'.