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- Find package directories better. Previously we used build.FindOnly
  which didn't work the way I expected it to (any dir would work w/o
  error).
- Set the VendorExperiment bool based on go version as 1.6 defaults to
  on.
- A bunch of extra debugging for use while sanity checking myself.
- vendor flag for test structs.
- Some tests for vendor/ stuff:
    - Basic Test
    - Transitive
    - Transitive, across GOPATHs + collapse vendor/ directories.

Should Fix #358