t4015: check "negative" case for "-w --color-moved"

t4015: check "negative" case for "-w --color-moved"

We test that lines with whitespace changes are not found by
"--color-moved" by default, but are found if "-w" is added.
Let's add one more twist: a line that has non-whitespace
changes should not be marked as a pure move.

This is perhaps an obvious case for us to get right (and we
do), but as we add more whitespace tests, they will form a
pattern of "make sure this case is a move and this other
case is not".

Note that we have to add a line to our moved block, since
having a too-small block doesn't trigger the "moved"
heuristics.  And we also add a line of context to ensure
that there's more context lines than moved lines (so the
diff shows us moving the lines up, rather than moving the
context down).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>