[MERGE][328007] Fixed problem with `log -p` and non-ascii content of files: show_diff should write the diff to exact [stdout] stream.

[Alexander Belchenko]

This patch provides fix for bug #328007: log -p on non-ascii files crashed with unicode error.
I wrote this patch by Ian request (actually I wrote 2 variants of patch).
Now I've added simple smoke test. This test failed with unicode error without my patch
and succeed with it.
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