fix typos, mostly in comments

Lib/test/test_dircache.py

@@ -46,7 +46,7 @@ class DircacheTests(unittest.TestCase):
 
         if sys.platform[:3] not in ('win', 'os2'):
             # Sadly, dircache has the same granularity as stat.mtime, and so
-            # can't notice any changes that occured within 1 sec of the last
+            # can't notice any changes that occurred within 1 sec of the last
             # time it examined a directory.
             time.sleep(1)
             self.writeTemp("test1")

Lib/test/test_threadsignals.py

@@ -21,7 +21,7 @@ def registerSignals((for_usr1, for_usr2, for_alrm)):
     return usr1, usr2, alrm
 
 
-# The signal handler. Just note that the signal occured and
+# The signal handler. Just note that the signal occurred and
 # from who.
 def handle_signals(sig,frame):
     signal_blackboard[sig]['tripped'] += 1