Merge lexical_cast from trunk:

* Deduce stream character type for user defined classes (fixes #6786)
* Deprecated macros replaced with new ones (thanks to Marshall Clow)
* Updated documentation (refs #6786, fixes #7582)
* More tests and minor bugfixes

[SVN r81668]

test/lexical_cast_loopback_test.cpp

@@ -86,7 +86,11 @@ void test_round_conversion_double()
 
 void test_round_conversion_long_double()
 {
+// We do not run tests on compilers with bugs
+#ifndef BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS
     test_round_conversion<long double>();
     test_msvc_magic_values<long double>();
+#endif
+    BOOST_CHECK(true);
 }