Reimport misc/xtide to time/

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diff --git a/time/xtide/DESCR b/time/xtide/DESCR
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+XTide is a package that provides tide and current predictions in a
+wide variety of formats.  Graphs, text listings, and calendars can be
+generated, or a tide clock can be provided on your desktop.  XTide can
+work with X-windows, plain text terminals, or the web.  This is
+accomplished with three separate programs:  the interactive interface
+(xtide), the non-interactive or command line interface (tide), and the
+web interface (xttpd).
+
+The algorithm that XTide uses to predict tides is the one used by the
+National Ocean Service in the U.S.  It is significantly more accurate
+than the simple tide clocks that can be bought in novelty stores.
+However, it takes more to predict tides accurately than just a spiffy
+algorithm -- you also need some special data for each and every
+location for which you want to predict tides.  XTide reads this data
+from harmonics files.  Ultimately, XTide's predictions can only be as
+good as the available harmonics data.  Due to issues of data
+availability and of compatibility with non-U.S.  tide systems, the
+predictions for U.S.  locations tend to be a lot better on average
+than those for locations outside of the U.S.
+* Deviations of 1 minute from official predictions are typical for U.S.
+  locations having the latest data.
+* Deviations of 20 minutes are typical for non-U.S. locations or U.S.
+  locations that are using obsolete data.
+* Much longer deviations indicate a problem.