New feature: creating a directory tree

[blerner]

Implements a new method create-dir-tree, which is like mkdir -p but enhanced. Given a base directory, and a string-dict of string-dicts of ..., where the innermost string-dicts' values are irrelevant, build a directory tree whose nesting structure corresponds to the keys of the string-dicts.

[shriram]

WHOA.

What does this do in the browser?

[blerner]

Nothing -- it's in the filelib module, which isn't made available on CPO.