Changelog:
   - remove hosts, host_strs and host_hdr from sg's
     procfs interface **
   - add sysfs interface for allow_dio, def_reserved_size
     and version ***
   - switch boot time and module parameters to Rusty's
     moduleparam.h interface. This means, for example,
     the boot time "sg_def_reserved_size" parameter
     changes to "sg.def_reserved_size".


** Christoph moved the host listing functionality into
    a more central sysfs position (i.e. not dependent on
    sg). However scsi_debug is the only LLD that I can
    get to post any "host" info under the new arrangement.

    Should devices, device_strs and device_hdrs also be
    moved out of sg's procfs interface?

*** I find sg's "debug" in its procfs interface very
     useful for debugging (sg itself amongst other things).
     However it does not seem suitable for sysfs. Should
     it move?