…f existing abstractions.

Correct silly typo in unchecked_factorial.hpp.
Remove TEST_STD define in config.hpp as it needlessly breaks the TR1 tests.
Remove lexical_cast.hpp workaround file.
Correct #pragma in tr1.hpp.

Stop referencing boost::lexical_cast even in templates which aren't instantiated.
Fix missing macro definition in tr1.hpp.
Correct include order in some tests so we get consistent definitions for BOOST_HAS_FLOAT128.

[CI SKIP]