Indent and sort keys in the JSON manifest.

This makes it easier to incorporate under version control since the file
is less likely to change, and if so, can be diffed/merged more easily.
Merge pull request #247 from nvie/master

Indent and sort keys in the JSON manifest
Use properly resolved target for auto mkdir.

The code that automatically created the target directory was still using a
simple path.join() rather than the resolver.