exclude OPTIONS requests from throttling

Browsers send OPTIONS requests an API server prior to every request to check if CORS allowed, so rates are reached half time. We could just double the rate, but other clients don't send extra requests.

rest_framework/throttling.py

@@ -118,6 +118,9 @@ class SimpleRateThrottle(BaseThrottle):
         """
         if self.rate is None:
             return True
+            
+        if request.method == 'OPTIONS':
+            return True
 
         self.key = self.get_cache_key(request, view)
         if self.key is None: