Add new debugfs commands and arguments which make it easier to

Add new debugfs commands and arguments which make it easier to
recover deleted files.  The lsdel command now takes an optional
argument which allows the user to only see the most recently
deleted files.  Also added a new command, undel, which automates
undeleting a deleted inode and linking it back to a directory.
Also added an optional count argument to the testb, freeb, setb,
and find_free_block commands.  The ls command now takes a new
option, -d, which lists deleted directory entries.

Factored out out commonly used code into utility subroutines
for ease of maintenance and to make the executable size smaller.