R1:9c925464baf8

Default "environment.append-paths" to include likely paths

Summary:
A few more of these issues have cropped up recently. Basically:

- Webservers often (by default, I guess?) have a different or nonexistent $PATH.
- Users have a hard time figuring this out, since it's not obvious that the webserver might have a different configuration than the CLI, and they can run "git" and such themselves fine, and they don't normally use SetEnv or similar in webserver config.

I've been pursuing one prong of attack…