Blocked revisions 71663 via svnmerge

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  r71663 | mark.dickinson | 2009-04-16 20:52:09 +0100 (Thu, 16 Apr 2009) | 15 lines

  Issue #1580: use short float repr where possible.
   - incorporate and adapt David Gay's dtoa and strtod
     into the Python core
   - on platforms where we can use Gay's code (almost
     all!), repr(float) is based on the shortest
     sequence of decimal digits that rounds correctly.
   - add sys.float_repr_style attribute to indicate
     whether we're using Gay's code or not
   - add autoconf magic to detect and enable SSE2
     instructions on x86/gcc
   - slight change to repr and str:  repr switches
     to exponential notation at 1e16 instead of
     1e17, str switches at 1e11 instead of 1e12
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