fix recurring typo: occured --> occurred

src/ZEO/Exceptions.py

@@ -16,7 +16,7 @@
 from ZODB.POSException import StorageError
 
 class ClientStorageError(StorageError):
-    """An error occured in the ZEO Client Storage."""
+    """An error occurred in the ZEO Client Storage."""
 
 class UnrecognizedResult(ClientStorageError):
     """A server call returned an unrecognized result."""

src/ZODB/FileStorage/FileStorage.py

@@ -890,7 +890,7 @@ class FileStorage(BaseStorage.BaseStorage,
                 self._file.write(p64(tl))
                 self._file.flush()
             except:
-                # Hm, an error occured writing out the data. Maybe the
+                # Hm, an error occurred writing out the data. Maybe the
                 # disk is full. We don't want any turd at the end.
                 self._file.truncate(self._pos)
                 raise

src/ZODB/POSException.py

@@ -31,7 +31,7 @@ class POSKeyError(KeyError, POSError):
         return oid_repr(self.args[0])
 
 class TransactionError(POSError):
-    """An error occured due to normal transaction processing."""
+    """An error occurred due to normal transaction processing."""
 
 class TransactionFailedError(POSError):
     """Cannot perform an operation on a transaction that previously failed.
@@ -252,7 +252,7 @@ class UndoError(POSError):
         return _fmt_undo(self._oid, self._reason)
 
 class MultipleUndoErrors(UndoError):
-    """Several undo errors occured during a single transaction."""
+    """Several undo errors occurred during a single transaction."""
 
     def __init__(self, errs):
         # provide a reason and oid for clients that only look at that

src/transaction/_transaction.py

@@ -443,7 +443,7 @@ class Transaction(object):
                 # TODO: do we need to make this warning stronger?
                 # TODO: It would be nice if the system could be configured
                 # to stop committing transactions at this point.
-                self.log.critical("A storage error occured during the second "
+                self.log.critical("A storage error occurred during the second "
                                   "phase of the two-phase commit.  Resources "
                                   "may be in an inconsistent state.")
                 raise