python access to driver namespace, rather then have a textblock defined for drivers allow scripts to add functions directly.

- bpy.app.driver_namespace, read-only dictionary, edit in-place.
- reset on file load and new file.
- on errors the namespace used to be reset, this should not be needed.

simple example.

  def driverFunc(val):
    return val * val
  bpy.app.driver_namespace['driverFunc'] = driverFunc

... now all drivers can access this function.

source/blender/python/intern/bpy_app.h

@@ -28,4 +28,8 @@
 
 PyObject *BPY_app_struct( void );
 
+/* bpy_driver.c */
+int bpy_pydriver_create_dict(void);
+extern PyObject *bpy_pydriver_Dict;
+
 #endif