Include necessary header, don't rely on two-phase lookup not being there.

Fixes #6790.


[SVN r78331]

Author: vprus

include/boost/program_options/detail/config_file.hpp

@@ -17,9 +17,7 @@
 #include <boost/program_options/eof_iterator.hpp>
 
 #include <boost/detail/workaround.hpp>
-#if BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3202))
 #include <boost/program_options/detail/convert.hpp>
-#endif
 
 #if BOOST_WORKAROUND(__DECCXX_VER, BOOST_TESTED_AT(60590042))
 #include <istream> // std::getline