Context

This is an addition to #228
I think that "strict" mode should behave like "once" mode when the requested cassette does not exist.
The original "strict" implementation has no way to record initial cassettes.
When I need a new cassette (e.g. I create a new TestCase), I have to change my code to setMode('once'), create the cassette, and then change my code back to setMode('strict').
I'm submitting this as a separate pull request, because #228 was supposed to be only a style-cleaned version of the original #160. This is a functional change from that PR.

What has been done

• If cassette is new, then "strict" mode behaves like "once" mode

How to test

• setMode('strict')
• Insert a non-existent cassette
• Trigger a request (curl, stream wrapper, etc)
• Fail!

Todo

• N/A

Notes

• N/A