[m-dev.] diff: runtime cleanup continued.

[Zoltan Somogyi]

> runtime/*.h:
> runtime/*.c:
> runtime/mercury_conf.h.in:
> 	Remove old .h files.
> 	Update #includes to refer to mercury_*.h
> 	Update #ifdef MODULE_H to be #ifdef MERCURY_MODULE_H

It might be a good idea to rename imp.h not to mercury_imp.h but to
something like mercury_runtime.h. The name imp.h was a historical
accident; it does not mean anything relevant to Mercury today.

Zoltan.