keep_alive call policy (analogous to Boost.Python's with_custodian_and_ward, fixes #62)

CMakeLists.txt

@@ -109,6 +109,7 @@ add_library(example SHARED
   example/example10.cpp
   example/example11.cpp
   example/example12.cpp
+  example/example13.cpp
 )
 
 # Don't add a 'lib' prefix to the shared library
@@ -179,7 +180,7 @@ endif()
 
 enable_testing()
 set(RUN_TEST ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/example/run_test.py)
-foreach(i RANGE 1 12)
+foreach(i RANGE 1 13)
   add_test(NAME example${i} COMMAND ${RUN_TEST} example${i})
 endforeach()