This commit adds a new set of sharness tests for pinning, and addresses
bugs that were pointed out by said tests.

test/sharness: added more pinning tests

Pinning is currently broken. See issue #1051. This commit introduces
a few more pinning tests. These are by no means exhaustive, but
definitely surface the present problems going on. I believe these
tests are correct, but not sure. Pushing them as failing so that
pinning is fixed in this PR.

make pinning and merkledag.Get take contexts

improve 'add' commands usage of pinning

FIXUP: fix 'pin lists look good'

ipfs-pin-stat simple script to help check pinning

This is a simple shell script to help check pinning.

We ought to strive towards making adding commands this easy.
The http api is great and powerful, but our setup right now
gets in the way. Perhaps we can clean up that area.

updated t0081-repo-pinning

- fixed a couple bugs with the tests
- made it a bit clearer (still a lot going on)
- the remaining tests are correct and highlight a problem with
  pinning. Namely, that recursive pinning is buggy. At least:
  towards the end of the test, $HASH_DIR4 and $HASH_FILE4 should
  be pinned indirectly, but they're not. And thus get gc-ed out.
  There may be other problems too.

cc @whyrusleeping

fix grep params for context deadline check

fix bugs in pin and pin tests

check for block local before checking recursive pin