Small update for pydrivers: force reloading the pydrivers.py Blender

text module when user edits the input text box of any pydriver
(Transform Properties panel, Ipo window).

It's enough to click in and out of a single pydriver's text input box
for the module reloading and also re-evaluation of all pydrivers
available. Maybe this "refreshing" should also be available from a
menu, let's see.

Note for Python fans:

Definitions and redefinitions in a reloaded module are properly handled
in Python, but previously defined data in the module doesn't disappear.
So if you define a function "f" inside a module, import it, then change
the function's name to "g" and reload the module, both "f" and "g" will
be available. This is considered a feature, check reload's documentation:
http://docs.python.org/lib/built-in-funcs.html#l2h-59

source/blender/python/BPY_interface.c

@@ -1021,6 +1021,7 @@ static float pydriver_error(IpoDriver *driver) {
 		bpy_pydriver_freeList();
 
 	if (bpy_pydriver_Dict) { /* free the global dict used by pydrivers */
+		PyDict_Clear(bpy_pydriver_Dict);
 		Py_DECREF(bpy_pydriver_Dict);
 		bpy_pydriver_Dict = NULL;
 	}
@@ -1034,6 +1035,21 @@ static float pydriver_error(IpoDriver *driver) {
 	return 0.0f;
 }
 
+/* Update function, it gets rid of pydrivers global dictionary, forcing
+ * BPY_pydriver_eval to recreate it. This function is used to force
+ * reloading the Blender text module "pydrivers.py", if available, so
+ * updates in it reach pydriver evaluation. */
+void BPY_pydriver_update(void)
+{
+	if (bpy_pydriver_Dict) { /* free the global dict used by pydrivers */
+		PyDict_Clear(bpy_pydriver_Dict);
+		Py_DECREF(bpy_pydriver_Dict);
+		bpy_pydriver_Dict = NULL;
+	}
+
+	return;
+}
+
 /* for depsgraph.c, runs py expr once to collect all refs. made
  * to objects (self refs. to the object that owns the py driver
  * are not allowed). */