Class headers should already be stand-alone, so include them first.

The trigger is OS X's broken (old) standard library which doesn't
undefine the toupper, tolower, etc. macros from ctypes.h when declaring
the std::toupper family of C++ functions which causes errors for the
locale overloads (the macros only take one argument).

Change-Id: Ia51b633abf44747a5ba603044da37c0786eebed9