Add CMake variable to choose Python version.

CMakeLists.txt

@@ -43,7 +43,11 @@ ENDIF(APPLE)
 
 # {{{ C++ and Python client.
 # Dependencies
-FINDPYTHON()
+IF(DEFINED PYTHON_DESIRED_VERSION)
+  FINDPYTHON(${PYTHON_DESIRED_VERSION} EXACT)
+ELSE()
+  FINDPYTHON()
+ENDIF()
 ADD_REQUIRED_DEPENDENCY("omniORB4 >= 4.1.4")
 
 SET(${PROJECT_NAME}_HEADERS