Use ::QueryPerformanceCounter() for wxStopWatch implementation in wxMSW.

QueryPerformanceCounter() provides higher resolution and precision for
measuring time under MSW, even though it suffers from some problems in older
Windows versions.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69834 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/stopwatch.h

@@ -25,6 +25,13 @@
         wxLogMessage("And calling it twice took $ldms in all", sw.Time());
     @endcode
 
+    Since wxWidgets 2.9.3 this class uses @c ::QueryPerformanceCounter()
+    function under MSW to measure the elapsed time. It provides higher
+    precision than the usual timer functions but can suffer from bugs in its
+    implementation in some Windows XP versions. If you encounter such problems,
+    installing a Microsoft hot fix from http://support.microsoft.com/?id=896256
+    could be necessary.
+
     @library{wxbase}
     @category{misc}