- Split tests into three rough categories. - Use fesetround() instead of fpsetround(), and add tests for   various rounding modes. - Test that all NaNs generated are quiet.
- Split tests into three rough categories.
- Use fesetround() instead of fpsetround(), and add tests for
  various rounding modes.
- Test that all NaNs generated are quiet.

Some of these tests won't pass until problems in vendor sources
(gdtoa and gcc) are fixed and new versions imported, but I
want to get these changes into the tree before I accidentally
blow them away again.  :-(

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