2012-12-31 issue:103,bug fixed in disk_io.c(grub_open func filename length limitation).
2012-12-30 (sha0)Added "map --report-eltorito=DEVICE" function

The 'map' command now accepts a new option
'--report-eltorito=DEVICE', where DEVICE determines which
INT 0x13 drive number will be reported to users of the
El Torito INT 0x13, AX=0x4B01 function, regardless of the
value of the DL register.  There are such users including
(but not limited to) the ElTorito.sys DOS driver included
with Syslinux (in dosutil/).  The INT 0x13 hook must be
established with at least one virtual optical disc drive
before this command option is used.

Example: map (hd0,0)/some.iso (0xA0)
         map --hook
         map --report-eltorito=(0xA0)

Signed-off-by: Shao Miller <sha0.miller@gmail.com>