Add decorator versions of the various wait functions

[idanarye]

I've noticed this common pattern:

def foo(self, a, b, c, timeout=60):
    def pred():
	...
    wait(timeout, pred, message=False)

These new decorators can be used to remove this boilerplate:

@waiting(timeout=60)
def foo(self, a, b, c):
    ...

[koreno]

seems like there's a stray print call.
also I think the __make_waiting_decorator and __waiting_decorator could use some high-level commenting so we can tell what the code intends to be doing.

[koreno]

print?