Increase line coverage of webmachine unit and integration tests. The

goal for this first round is to increase coverage of the decision core
of webmachine. For each node on the v3 HTTP activity diagram there are
one or more tests that reach that node.

There are tests to cover 406, 412, 401, 400, 301, 307, 304, 404, 201,
409, 303, 202, 200, 201, 410, 300, 500, 501, 403, 414, 415, 413,
including Vary headers, streaming bodies, MD5 sums.

Additionally, extra logging and archiving have been added to access
data on Travis CI.

Some of the previously existing tests have been fixed, as well as a
minor bug in webmachine itself.