https://issues.dlang.org/show_bug.cgi?id=14294

          Issue ID: 14294
           Summary: partialSort should also accept two ranges
           Product: D
           Version: D2
          Hardware: x86
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: Phobos
          Assignee: nobody@puremagic.com
          Reporter: andrei@erdani.com

... just like topN.

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