Suggested tune/tuneup.c patch

[Torbjörn Granlund]

  And please take a screenshot of the affected parameters before and
  after this change, as a sanity check.

I added a history preservation feature to the .../devel/thres/ pages.  At
23:59 each night, all pages are copied to .../devel/thres/YYYY-MM-DD.

(There is no index, one needs to type in the wanted date manually.)

-- 
Torbjörn
Please encrypt, key id 0xC8601622