Added timestamp maximum

Author: vub

ethereum/blocks.py

@@ -414,6 +414,8 @@ def __init__(self, header, transaction_list=[], uncles=[], env=None,
                 raise ValueError("Gas used exceeds gas limit")
             if self.timestamp <= parent.header.timestamp:
                 raise ValueError("Timestamp equal to or before parent")
+            if self.timestamp >= 2**256:
+                raise ValueError("Timestamp waaaaaaaaaaayy too large")
 
         for uncle in uncles:
             assert isinstance(uncle, BlockHeader)