vchoi_fork

[svn-r11311] Purpose: New features.

Description:  Added 2 new configure options, --enable-exception and --enable-accuracy.

--enable-exception lets the library check whether user's exception handling
functions are present during compiler data conversions and use them if they are.
When it's disabled, this step is skipped to improve conversion speed.  This
step isn't implemented yet for soft conversions because there would be little
gain in speed.

--enable-accuracy guarantees data accuracy during data conversions.  It means
the library will choose compiler conversions only if the accurate data is
secured.  Otherwise, the library will go for the library's own conversions.  If
this option is disabled, the library uses compiler conversions in favor of
their speed as long as they work even if data can be incorrect.


Platforms tested: h5committest and fuss.  Some systems may fail after this
checkin.