DJB Redo

DJB Redo is the original spec for "redo." But you will need apenwarr/redo to actually use it.

• redo: always rebuild a target
• redo-ifchange: rebuild target if out of date
• Build to new temp file and replace: otherwise the file on the system is trunacated, out of date, incorrect. On system failure it looks like the unfinished file still exists.
• Use normal binaries to talk to the system: redo-ifchange is just an executable run from shell scripts.
• Let shell scripts handle any special logic: they run redo-ifchange and friends as needed.
• Put environment configs in files, add redo-ifchange before importing them.