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_extern.h

@@ -81,6 +81,7 @@ extern "C" {
 	int BPY_do_spacehandlers(struct ScrArea *sa, unsigned short event,
 		unsigned short space_event);
 
+	void BPY_pydriver_update(void);
 	float BPY_pydriver_eval(struct IpoDriver *driver);
 	struct Object **BPY_pydriver_get_objects(struct IpoDriver *driver);