shiboken: install to the generic library path

Projects/shiboken.cmake

+set(shiboken_args)
+if (UNIX)
+  list(APPEND shiboken_args
+    -DPYTHON_SITE_PACKAGES:STRING=lib/python2.7/site-packages)
+endif ()
+
 add_external_project(shiboken
   DEPENDS qt python
   CMAKE_ARGS
@@ -5,5 +11,6 @@ add_external_project(shiboken
     -DSET_RPATH:BOOL=ON
     -DBUILD_SHARED_LIBS:BOOL=ON
     -DDISABLE_DOCSTRINGS:BOOL=ON
-	-DBUILD_TESTS:BOOL=OFF
+    -DBUILD_TESTS:BOOL=OFF
+    ${shiboken_args}
   )