Add first (print only) feature extractor

        * gcc_plugin/feature-extract.cpp: Define basic feature extractor.
        * gcc_plugin/gcc-plugin.cpp: Register feature extractor on launch.
        * gcc_plugin/mageec-plugin.h: Add register_featextract.
        * gcc_plugin/Makefile.am: Added feature-extract.cpp to libmageec_gcc.
        * gcc_plugin/Makefile.in: Regenerated.
Fix include guard for mageec-passes.h.

        * include/mageec-passes.h: Fix include guard.
Replace use of disable_plugin with PLUGIN_OVERRIDE_GATE.

        * gcc_plugin/gcc-callbacks.cpp (pass_type_str): Define pass to type
        conversion function.
        (mageec_pass_gate): Print pass information on gate override.
        * gcc_plugin/gcc-plugin.cpp (parse_arguments): Remove
        dumppasses=disable option.
        (plugin_init): Register mageec_pass_gate as PLUGIN_OVERRIDE_GATE.
        Remove use of disable_pass.
        * gcc_plugin/mageec-plugin.h (mageec_gcc_pass_info): Removed.
        (mageec_pass_gate): Declared.
        * gcc_plugin/plugin-info.cpp (mageec_gcc_pass_info): Removed.