Don't cache python extension build file names.

This allows to build with various Python versions by calling scons with
the Python version we want to build for. Not the very best solution, but
a working one.

SConstruct

@@ -17,7 +17,6 @@
 
 # Unfinished items:
 # * Qt binding (needs to build .pc, .prl files)
-# * Allow building for multiple python versions)
 # * Out-of-directory builds: see http://www.scons.org/wiki/UsingBuildDir
 
 # Release identification begins here
@@ -927,7 +926,13 @@ else:
     for ext, sources in python_extensions.iteritems():
         python_objects[ext] = []
         for src in sources:
-            python_objects[ext].append(python_env.SharedObject(src.split(".")[0] + '-py', src))
+            python_objects[ext].append(
+                python_env.NoCache(
+                    python_env.SharedObject(
+                        src.split(".")[0] + '-py_' + '_'.join(['%s' %(x,) for x in sys.version_info]), src
+                    )
+                )
+            )
         python_compiled_libs[ext] = python_env.SharedLibrary(ext, python_objects[ext])
     python_built_extensions = python_compiled_libs.values()