ENH: Add max leverage account guard

tests/resources/saved_state_archive/zipline.finance.blotter.Order/State_Version_1

@@ -48,7 +48,7 @@ p20
 I6
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-S'ca467b999ff148f4b4fa89aa2cd899a9'
+S'e837d6193375414eb1594c8adb068a34'
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tests/resources/saved_state_archive/zipline.finance.performance.position_tracker.PositionTracker/State_Version_1

@@ -4,142 +4,133 @@ p1
 (dp2
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 p3
+(dp4
+sS'unpaid_dividends'
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 BlockManager
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 I-1
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-(lp32
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 aS'payment_sid'
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 aS'cash_amount'
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 Ns.