Remove Phoenix v2 scaffolding.
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Since the introduction of Phoenix v3 (in boost 1.47) the 'result' struct is no longer needed in spirit parser. See eg. http://www.boost.org/doc/libs/1_47_0/libs/phoenix/doc/html/phoenix/what_s_new/phoenix_3_0.html which points out the switch to the 'Boost::Result_of' protocol