Don't explicitly link Python on OS X

Explicitly linking to a Python framework on OS X prevents modules from
being built against one python (i.e. system python) and imported from
another (i.e. Homebrew python); the interpreter segfaults if there's a
linkage to a foreign python. Building the module with `-undefined
dynamic_lookup` instead of an explicit link allows the symbols to be
resolved at load time from a compatible python.

modules/python/CMakeLists.txt

@@ -64,7 +64,11 @@ add_library(${the_module} SHARED src2/cv2.cpp ${CMAKE_CURRENT_BINARY_DIR}/genera
 if(PYTHON_DEBUG_LIBRARIES AND NOT PYTHON_LIBRARIES MATCHES "optimized.*debug")
   target_link_libraries(${the_module} debug ${PYTHON_DEBUG_LIBRARIES} optimized ${PYTHON_LIBRARIES})
 else()
-  target_link_libraries(${the_module} ${PYTHON_LIBRARIES})
+  if(APPLE)
+    set_target_properties(${the_module} PROPERTIES LINK_FLAGS "-undefined dynamic_lookup")
+  else()
+    target_link_libraries(${the_module} ${PYTHON_LIBRARIES})
+  endif()
 endif()
 target_link_libraries(${the_module} ${OPENCV_MODULE_${the_module}_DEPS})