Include request info when NotMatchError occurs

[goodgravy]

Problem

When investigating RequestNotMatchError exceptions, it can be hard to see where the problem is. The best approach seems to be to move your cassettes to one side, re-run the test, then diff the new and old cassettes to see where the change it.

This is a pretty slow and laborious developer experience.

Solution

Include some basic information about the request which didn't match anything in the active cassette, to help the developer zero in on where the problem is.

Example message:

Request did not match with any one in the current cassette: fixture/vcr_cassettes/example_ibrowse_different.json.
Delete the current cassette with [mix vcr.delete] and re-record.

Request: ['http://example.com/different_from_original', [], :get]

If there's a better way to format the request in a human-friendly way, let me know!

[coveralls]

Coverage increased (+0.02%) to 93.427% when pulling 412aeae on goodgravy:master into aa8d09d on parroty:master.

[parroty]

Thanks! and sorry taking time to merge.