in 5.1, find pathname for required module?

[nr@... (Norman Ramsey)]

I have a large installed based of Lua 5.1 code (about 75,000 lines),
and I've recently found it useful to write Lua code that is a lot
like Make rules.  This code needs to rebuild files when the code
itself has changed, so I need to get a timestamp on the file in 
which the code lives.  I see that in Lua 5.3, there are facilities
like `package.searchpath` and an extension to `require` (relative to 5.1)
that can pass an extra parameter.  Can anyone suggest a way to
replicate this functionality in 5.1?


Norman