Associating module symbols with defining files

[Spencer Baugh <sbaugh@janestreet.com>]

It's currently impossible to associate a symbol defined by a module with
the source file which actually defined that symbol.

If this were possible, things like help-view-source would be able to
jump to the source code for a module-defined function.  Under the hood,
ultimately we want symbol-file to return a correct filename for these
symbols.

Instead, currently, every symbol defined by a module is "defined" by the
module .so.  So jumping to source just jumps to the (compiled) .so,
which is fairly useless.

Could this be fixed?