Missing DEV_SD1_MAJOR in dtable.cc

[Loh, Joe]

Thank you so much Eric for setting us straight on submitting patches,
and Corinna for making change before we had a chance to followup with
Eric's recommendation.

We will be sorting out the necessary documentation in order to
submitting the non-trivial patch for mapping up to 64 volumes, as
pointed out by Eric.

One other behavior we noticed is that /proc/partition currently shows
multiple entries of /dev/sdz if number of volumes exceeds 26.  It's a
pretty benign behavior and we don't have any recommended patches.

Thank you all for your support of Cygwin.

Joe Loh