Add a test case exploring freeze behavior on an inactive console buffer
Add a test case exploring freeze behavior on an inactive console buffer

So far, I've only tested it on Windows 7.  The test passed on that OS:
creating a screen buffer isn't blocked by selection, but writing to an
inactive buffer *is* blocked, regardless of whether the buffer was created
before or after selection began.  The use of Mark or SelectAll doesn't
affect behavior.

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