Refactor unlimited allowance logic out of ERC20Token

packages/contracts/contracts/test/DummyToken_v2.sol

@@ -8,7 +8,7 @@ contract DummyToken_v2 is Mintable_v2, Ownable_v2 {
     string public symbol;
     uint public decimals;
 
-    function DummyToken(
+    function DummyToken_v2(
         string _name,
         string _symbol,
         uint _decimals,

packages/contracts/contracts/test/Mintable_v2.sol

@@ -1,13 +1,13 @@
 pragma solidity 0.4.18;
 
-import "./../tokens/ERC20Token.sol";
+import "./../tokens/UnlimitedAllowanceToken_v2.sol";
 import "./../lib/SafeMath_v2.sol";
 
 /*
  * Mintable
  * Base contract that creates a mintable UnlimitedAllowanceToken
  */
-contract Mintable_v2 is ERC20Token, SafeMath_v2 {
+contract Mintable_v2 is UnlimitedAllowanceToken_v2, SafeMath_v2 {
     function mint(uint _value) 
         public
     {

packages/contracts/contracts/tokens/ERC20Token.sol

@@ -1,11 +1,9 @@
-pragma solidity ^0.4.18;
+pragma solidity 0.4.18;
 
 import "./Token_v2.sol";
 
 contract ERC20Token is Token_v2 {
 
-    uint constant MAX_UINT = 2**256 - 1;
-
     function transfer(address _to, uint _value)
         public
         returns (bool) 
@@ -17,22 +15,14 @@ contract ERC20Token is Token_v2 {
         return true;
     }
 
-    /// @dev ERC20 transferFrom, modified such that an allowance of MAX_UINT represents an unlimited allowance. See https://github.com/ethereum/EIPs/issues/717
-    /// @param _from Address to transfer from.
-    /// @param _to Address to transfer to.
-    /// @param _value Amount to transfer.
-    /// @return Success of transfer.
     function transferFrom(address _from, address _to, uint _value)
         public 
         returns (bool) 
     {
-        uint allowance = allowed[_from][msg.sender];
-        require(balances[_from] >= _value && allowance >= _value && balances[_to] + _value >= balances[_to]); 
+        require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value >= balances[_to]); 
         balances[_to] += _value;
         balances[_from] -= _value;
-        if (allowance < MAX_UINT) {
-            allowed[_from][msg.sender] -= _value;
-        }
+        allowed[_from][msg.sender] -= _value;
         Transfer(_from, _to, _value);
         return true;
     }

packages/contracts/contracts/tokens/EtherToken_v2.sol

@@ -18,10 +18,10 @@
 
 pragma solidity 0.4.18;
 
-import "./ERC20Token.sol";
+import "./UnlimitedAllowanceToken_v2.sol";
 import "./../lib/SafeMath_v2.sol";
 
-contract EtherToken_v2 is ERC20Token, SafeMath_v2 {
+contract EtherToken_v2 is UnlimitedAllowanceToken_v2, SafeMath_v2 {
 
     string constant public name = "Ether Token";
     string constant public symbol = "WETH";
@@ -46,7 +46,7 @@ contract EtherToken_v2 is ERC20Token, SafeMath_v2 {
     }
 
     /// @dev Sells tokens in exchange for Ether, exchanging them 1:1.
-    /// @param amount Number of tokens to sell.
+    /// @param _value Number of tokens to sell.
     function withdraw(uint _value)
         public
     {

packages/contracts/contracts/tokens/UnlimitedAllowanceToken_v2.sol

@@ -0,0 +1,46 @@
+/*
+
+  Copyright 2017 ZeroEx Intl.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+*/
+
+pragma solidity 0.4.18;
+
+import "./ERC20Token.sol";
+
+contract UnlimitedAllowanceToken_v2 is ERC20Token {
+
+    uint constant MAX_UINT = 2**256 - 1;
+
+    /// @dev ERC20 transferFrom, modified such that an allowance of MAX_UINT represents an unlimited allowance. See https://github.com/ethereum/EIPs/issues/717
+    /// @param _from Address to transfer from.
+    /// @param _to Address to transfer to.
+    /// @param _value Amount to transfer.
+    /// @return Success of transfer.
+    function transferFrom(address _from, address _to, uint _value)
+        public 
+        returns (bool) 
+    {
+        uint allowance = allowed[_from][msg.sender];
+        require(balances[_from] >= _value && allowance >= _value && balances[_to] + _value >= balances[_to]); 
+        balances[_to] += _value;
+        balances[_from] -= _value;
+        if (allowance < MAX_UINT) {
+            allowed[_from][msg.sender] -= _value;
+        }
+        Transfer(_from, _to, _value);
+        return true;
+    }
+}

packages/contracts/test/ts/unlimited_allowance_token_v2.ts

@@ -14,7 +14,7 @@ const web3: Web3 = (global as any).web3;
 chaiSetup.configure();
 const expect = chai.expect;
 
-contract('ERC20Token', (accounts: string[]) => {
+contract('UnlimitedAllowanceTokenV2', (accounts: string[]) => {
     const config = {
         networkId: constants.TESTRPC_NETWORK_ID,
     };