New features: automatic dependency order and resumable builds

[hlship]

This patch adapts code previously implemented in-house as a hook.

It allows lein-sub to analyze the sub-projects and work out inter-dependencies and, from that, the build order.

It works around a bug in lein-cljsbuild.

It also makes build resumable; our project has 48 sub-projects, so being able to recover from minor problems and typos is very important.

[kumarshantanu]

@hlship Thanks for putting in so much meticulous work in the PR, though I need some time to understand the patch in its entirety. One thing I am curious to know is when/how does the inter-dependency resolution trigger. Is it always automatic, irrespective of whether the sub-projects are specified via :sub entry in project.clj or via the command-line? Is there a way to opt out of the automatic resolution?

[hlship]

I'll have answer for you in a bit ... busy week for me! Lacinia release, Clojure/West next week!

[hlship]

I may have a chance to get back to this tomorrow. Meanwhile, I may have found a problem on novel artifacts, not yet in a repository.

[hlship]

... now, where we we?

It's driven by the :sub key of the master project; it builds the dependency ordering file if it does not already exist (or is out of date) and then iterates in the order defined there.

I had closed this for a couple of reasons, one of which I can't reproduce, and was probably a problem when I was working with it. Basically, I was worried that ordering would fail if the dependencies weren't in the local repository, but that is not the case, so I think this is good to go.

[kumarshantanu]

@hlship I tried to test the PR by running cd subtest followed by lein sub clean. With lein-sub 0.3 I get the order [child child2], but with this PR the order I'm getting is [child2 child]. It appears the PR auto-discovers the order even though the order is specified in project.clj under the :sub key. What am I missing?