CMake: Fix building with separate build dir

When building the python SWIG bindings in a separate build dir,
the build needs the directory of the build include path to get
pdal/pdal_defines.h.

python/CMakeLists.txt

@@ -2,6 +2,7 @@ if (SWIG_FOUND)
     find_package(PythonLibs 2.4)
     include_directories(${PYTHON_INCLUDE_PATH})
     include_directories("${PDAL_SOURCE_DIR}/include")
+    include_directories("${PROJECT_BINARY_DIR}/include")
     set_source_files_properties(pdal.i PROPERTIES CPLUSPLUS ON)
     swig_add_module(pdal python pdal.i)
     swig_link_libraries(pdal ${PYTHON_LIBRARIES})