convert my fdiscard-stuff.c into blkdiscard.c and give it a UI
that matches the linux-util version.

comes in two forms: blkdiscard equivalent, and the (almost)
original interface i used (the "-s" option is conflicting and
i've switched to only the not yet implemented secure erase
option.) the only real difference is that "fdiscard" mode
requires the -R flag to do something, vs blkdiscard needs the
-n flag to not do anything.


not yet hooked into the build or sets. would like more testing
on it to be performed before doing that (but soon.)