The get-module-path function finds the compiled or source file corresponding
to a module; get-module-code reads and compiles the contents of this file.
This work is preparation for exporting more functionality from this module.
Renamed variables for clarity and to eliminate shadowing.
Turned lets into defines.
The `lazy-require' form expands to `define-runtime-module-path-index',
whch doesn't work right at phase levels other than 0. Work around the
problem by generating a submodule to hold the
`define-runtime-module-path-index' form.
This repair fixes `raco exe' on certain uses of `match', which in turn
uses `lazy-require' at compile time.
Also, use `register-external-module' to generate appropriate
dependencies on lazily loaded modules.
The new parameter (and supporting environment variables and
command-line flags) can bytecode lookup to a tree other than
where a source file resides, so that sources and generated
compiled files can be kept separate. It also supports storing
bytecode files in a version-specific location (either with
the source or elsewhere).
