Build Python 3 bindings in subdirectory

Build the Python 3 cv2 module in lib/python3/, to avoid potential naming
conflicts with the Python 2 bindings.

The Python 2 bindings are placed directly in lib/, where they are
required for the Buildbot to successfully execute the Python tests.

modules/python/common.cmake

@@ -72,7 +72,7 @@ execute_process(COMMAND ${PYTHON_EXECUTABLE} -c "import distutils.sysconfig; pri
                 OUTPUT_STRIP_TRAILING_WHITESPACE)
 
 set_target_properties(${the_module} PROPERTIES
-                      LIBRARY_OUTPUT_DIRECTORY  "${LIBRARY_OUTPUT_PATH}/${MODULE_NAME}"
+                      LIBRARY_OUTPUT_DIRECTORY  "${LIBRARY_OUTPUT_PATH}/${MODULE_INSTALL_SUBDIR}"
                       PREFIX ""
                       OUTPUT_NAME cv2
                       SUFFIX ${CVPY_SUFFIX})

modules/python/python2/CMakeLists.txt

@@ -4,6 +4,8 @@ endif()
 
 set(the_description "The python2 bindings")
 set(MODULE_NAME python2)
+# Buildbot requires Python 2 to be in root lib dir
+set(MODULE_INSTALL_SUBDIR "")
 
 set(PYTHON_INCLUDE_PATH ${PYTHON2_INCLUDE_PATH})
 set(PYTHON_NUMPY_INCLUDE_DIRS ${PYTHON2_NUMPY_INCLUDE_DIRS})
@@ -17,6 +19,7 @@ set(PYTHON_VERSION_MINOR ${PYTHON2_VERSION_MINOR})
 include(../common.cmake)
 
 unset(MODULE_NAME)
+unset(MODULE_INSTALL_SUBDIR)
 unset(PYTHON_INCLUDE_PATH)
 unset(PYTHON_NUMPY_INCLUDE_DIRS)
 unset(PYTHON_EXECUTABLE)

modules/python/python3/CMakeLists.txt

@@ -4,6 +4,7 @@ endif()
 
 set(the_description "The python3 bindings")
 set(MODULE_NAME python3)
+set(MODULE_INSTALL_SUBDIR python3)
 
 set(PYTHON_INCLUDE_PATH ${PYTHON3_INCLUDE_PATH})
 set(PYTHON_NUMPY_INCLUDE_DIRS ${PYTHON3_NUMPY_INCLUDE_DIRS})
@@ -17,6 +18,7 @@ set(PYTHON_VERSION_MINOR ${PYTHON3_VERSION_MINOR})
 include(../common.cmake)
 
 unset(MODULE_NAME)
+unset(MODULE_INSTALL_SUBDIR)
 unset(PYTHON_INCLUDE_PATH)
 unset(PYTHON_NUMPY_INCLUDE_DIRS)
 unset(PYTHON_EXECUTABLE)