Undo commit 95680ed: "Switch to using a separate lockfile per target."
Undo commit 95680ed: "Switch to using a separate lockfile per target."

This was required for old versions of MacOS X, but the bug has now been
fixed, so let's de-clutter the .redo directory by reducing to a single
lock file instead of one per fid.

This reverts commit 08b05fd72f92fa0061b3d082b391151b43cd7497.

apenwarr/redo,apenwarr/redo,apenwarr/redo,apenwarr/redo