Data-only pg_rewind, take 2

Hi;

Attached is my second attempt at the pg_rewind change which allows one to
include only a minimal set. To my understanding, all past feedback has
been addressed.

The current patch does not change default behavior at present. It does add
a --data-only flag which allows pg_rewind to only rewind minimal files to
work. I believe this would generally be a good practice though maybe there
is some disagreement on that.

I have not run pg_indent because of the large number of other changes but
if that is desired at some point I can do that.

I also added test cases and some docs. I don't know if the docs are
sufficient. Feedback is appreciated. This is of course submitted for v13.

--
Best Regards,
Chris Travers
Head of Database

Tel: +49 162 9037 210 | Skype: einhverfr | www.adjust.com
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