Honour a watch delay of forever (fix: lepture#125)

Ensure that a delay value of `forever` gets added to the list of
returned delays so that we can prevent certain watch events from
triggering a reload.

This is essentially just implementing the work-around proposed by @dwt

ref: lepture#125 (comment)

livereload/watcher.py

@@ -101,7 +101,7 @@ def examine(self):
             if changed:
                 func = item['func']
                 delay = item['delay']
-                if delay and isinstance(delay, float):
+                if delay and isinstance(delay, float) or delay == 'forever':
                     delays.add(delay)
                 if func:
                     name = getattr(func, 'name', None)