Add symlink creation function (unused)

An earlier implementation needed the creation of symlinks, but this
implementation was changed to avoid that.  However, leave the libc
binding in case it is needed in the future.
Improve undelete searches (individual files).  Add new function.

The algorithm for searching for deleted files of specific names can
turn up the same transaction ID multiple times, and also it checks
transaction IDs out of order.  Update the logic to skip TIDs
that are older than the latest successful TID.

Also add a function to produce a timestamp based on the modification
time.  This is used for deleted directories in a future commit.
Free up "slide" cursor windows after use
Add search-directory capability

Now when slider is passed the pass of an existing directory, that
directory's history will be searched for all deleted files and
subdirectories that can be resurrected.  The undelete candidates will
be listed in two groups (directories first) and selectable.

If selected, a file can be undeleted or saved to a new filename.  A
selected directory can be completely restored or saved to a new
directory.

What is still missing is the ability to browse a deleted directory
to see what files are in it (but the individual files won't be
browsable.