A start at originally-proposed routine

Didn't get it working right, primarily w.r.t. files/dirs.
Also segfaulted.
Moved filerator code to modules+runtime

Everything still seems to work
Added test regarding following symbolic links

Because it turned out that I hadn't handled this case previously.
Commented Filerator iterators and added symbolic link support

I hadn't noticed that I hadn't added symbolic link support
prior to this.  Doing so now.
Split chpldirent.h into two files; renamed chpldirent.c

The chpldirent.* files were not so well named anymore, so
split the headers intwo two files:

* chpldirent.h : wraps dirent capabilities
* chplisdir.h  : provides the "is this a directory" predicate

Then renamed chpldirent.c because it only provided the predicate
and had nothing to do with dirent.