remove Firefox warning about prototype overwrite

Author: darkdarkdragon

src/currency.js

@@ -22,7 +22,7 @@ var Currency = extend(function() {
   this._update();
 }, UInt160);
 
-Currency.prototype = extend({}, UInt160.prototype);
+Currency.prototype = Object.create(extend({}, UInt160.prototype));
 Currency.prototype.constructor = Currency;
 
 Currency.HEX_CURRENCY_BAD = '0000000000000000000000005852500000000000';

src/seed.js

@@ -19,7 +19,7 @@ const Seed = extend(function() {
 }, UInt);
 
 Seed.width = 16;
-Seed.prototype = extend({}, UInt.prototype);
+Seed.prototype = Object.create(extend({}, UInt.prototype));
 Seed.prototype.constructor = Seed;
 
 // value = NaN on error.

src/uint128.js

@@ -13,7 +13,7 @@ var UInt128 = extend(function() {
 }, UInt);
 
 UInt128.width = 16;
-UInt128.prototype = extend({}, UInt.prototype);
+UInt128.prototype = Object.create(extend({}, UInt.prototype));
 UInt128.prototype.constructor = UInt128;
 
 var HEX_ZERO = UInt128.HEX_ZERO = '00000000000000000000000000000000';

src/uint160.js

@@ -17,7 +17,7 @@ var UInt160 = extend(function() {
 }, UInt);
 
 UInt160.width = 20;
-UInt160.prototype = extend({}, UInt.prototype);
+UInt160.prototype = Object.create(extend({}, UInt.prototype));
 UInt160.prototype.constructor = UInt160;
 
 var HEX_ZERO = UInt160.HEX_ZERO = '0000000000000000000000000000000000000000';

src/uint256.js

@@ -13,7 +13,7 @@ var UInt256 = extend(function() {
 }, UInt);
 
 UInt256.width = 32;
-UInt256.prototype = extend({}, UInt.prototype);
+UInt256.prototype = Object.create(extend({}, UInt.prototype));
 UInt256.prototype.constructor = UInt256;
 
 var HEX_ZERO = UInt256.HEX_ZERO = '00000000000000000000000000000000' +