internal/v4: add hash mismatch test
Merge pull request #66 from rogpeppe/032-v4-hash-mismatch-test

internal/v4: add hash mismatch test

This adds a more end-to-end test following the blobstore logic change.
internal/router: add method argument to meta handlers
internal/v4: add method arg to meta handlers
Merge pull request #67 from rogpeppe/033-meta-add-method

internal/router: add method argument to meta handlers

This will eventually enable us to PUT to meta endpoints.
Specific support for PUT will be added in a subsequent CL.