#6 boost version integration

[kbinani]

scons install failed with messages:

/usr/local/include/cppdom-1.2.0/cppdom/SpiritParser.h:51:10: fatal error: 'boost/spirit/core.hpp' file not found
#include <boost/spirit/core.hpp>
         ^
1 error generated.
scons: *** [build.darwin/type-optimized--arch-x64/cppdom/SpiritParser.o] Error 1
scons: building terminated because of errors.

on MacOSX10.9.4, Xcode 5.1.1.

The directory structure of boost::spirit library had changed since boost 1.50,
so we have to update #include.