WIP: HashFromNode and VerifyDepTree methods

[karrick]

What does this do / why do we need it?

HashFromNode creates a cryptographic digest (using SHA-256) of the directory rooted at the specified pathname. This can be used to address #121.

VerifyDepTree verifies the dependency tree against a map of known dependencies, along with file system nodes that were not expected to be found.

What should your reviewer look out for in this PR?

Function signatures do not exactly match what @sdboyer requested.

Do you need help or clarification on anything?

Which issue(s) does this PR fix?

These functions were requested in order to address #121, however might serve to address #944 as well.

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[karrick]

I signed it!

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[karrick]

When I was developing in my own fork, I had to change the internal exports to point to my own fork's copy: s|golang/dep|karrick/dep|g. The final commit before I submitted the PR, 27c0c77, changes all of the internal imports back to golang/dep.

I'm not certain why that particular commit is being shown as not included, but it's causing the build tests to fail, because the final commit is necessary to change the internal imports back to the original directories.

[karrick]

Looking at the Details from continuous-integration/appveyor/pr output, I recognized that I had omitted changing one of the internal import statements back to golang/dep. I fixed that, performed an additional audit of all the files in karrick/dep master to ensure no other instances were found, and pushed the commit to karrick/dep master, but before Travis CI build finished.

I would like to force kick off a new build of continuous-integration/appveyor/pr to verify it passes, but am unsure how. Instead, I plan on waiting for all of the other tests to finish, then if the failed test has not automatically executed, then I will push a small change to karrick/dep master, in hopes of kicking off a new build and tests.

[karrick]

Closed this PR, and will open a new one after I add a few more tests.

[sdboyer]

When I was developing in my own fork, I had to change the internal exports to point to my own fork's copy: s|golang/dep|karrick/dep|g

yeah, this is one of those annoying things. the standard practice (or at least, what i do) is to just set up my own fork as an alternate remote, then work on it directly in the canonical location on GOPATH.

IOW:

[~/w/go/s/gi/gol/dep] git remote -v
origin	git@github.com:sdboyer/dep (fetch)
origin	git@github.com:sdboyer/dep (push)
upstream	git@github.com:golang/dep.git (push)
upstream	git@github.com:golang/dep.git (fetch)