message: tests: Fix test fallout for MSVC6
  One more XPath test falls prey to MSVC6 NaN comparison codegen issues.
diff: @@ -661,7 +661,9 @@ TEST_XML(xpath_variables_type_conversion, "<node>15</node>")
  CHECK_XPATH_BOOLEAN_VAR(xml_node(), STR("string($b) = '42'"), &set, true);
  CHECK_XPATH_BOOLEAN_VAR(xml_node(), STR("boolean($c) = true()"), &set, true);
  +#ifndef MSVC6_NAN_BUG
  CHECK_XPATH_BOOLEAN_VAR(xml_node(), STR("number($c) = 0"), &set, false);
  +#endif
  CHECK_XPATH_BOOLEAN_VAR(xml_node(), STR("string($c) = 'test'"), &set, true);
  CHECK_XPATH_BOOLEAN_VAR(xml_node(), STR("boolean($d) = true()"), &set, true);
  