Lots of small changes to make tools/build-all.sh work under Mac OS X.

I've commented out (for now) the awk invocation in `tools/build-site.sh` because `dev2build-html.awk` is not in this repo.

I removed the use of globstar which doesn't exist on Mac OS X and which didn't seem to be needed.

Lots of other little things to make this cleaner or safer, e.g., don't try to `rm -fr /` when `readlink` fails on a mac :-).

Fixes #4