[boost] [numeric/conversion] fixes for intel-win32-7.1-vc6

These are trivial fixes taking care of BOOST_NO_STDC_NAMESPACE. With them, converter_test and udt_support_test (the latter is currently marked as known fail) work for Intel 7.1. OK to commit? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo 33a34

#if !defined(BOOST_NO_STDC_NAMESPACE) 35a37,38 #endif

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#if !defined(BOOST_NO_STDC_NAMESPACE) 55c59 <

#endif 81a86 #if !defined(BOOST_NO_STDC_NAMESPACE) 82a88,89 #endif

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#if !defined(BOOST_NO_STDC_NAMESPACE) 98a107,108 #endif

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#if !defined(BOOST_NO_STDC_NAMESPACE)

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#endif