mdiskchk: Support three new features

mdiskchk: Support three new features

MDISKCHK.COM now supports three new modes:

mdiskchk.com --mbfts
  This mode will scan between free base memory and
  0xA00000 looking for MEMDISK mBFTs.  For each one
  found, its detail will be reported.

mdiskchk.com --safe-hooks
  This mode will attempt to walk the chain of INT 13h
  "safe hooks".  For each MEMDISK "safe hook" found,
  its detail will be reported.

mdiskchk.com --batch-output
  This mode suppresses the normal detail report and
  instead outputs a list of DOS SET commands.  This
  is useful if one wishes to populate a batch file
  and call that batch file to set DOS environment
  variables, so that programs have access to those
  MEMDISK kernel arguments passed at boot-time.

These command-line options may be combined.

For example, your AUTOEXEC.BAT might go:
  @echo off
  echo @echo off>setenv.bat
  mdiskchk.com -m -s -b>>setenv.bat
  call setenv.bat>nul

Signed-off-by: Shao Miller <shao.miller@yrdsb.edu.on.ca>