Don't mutate the elliptic curve prototype with get* additions

Point's prototype is set to the prototype of ec('secp256k1').curve.point(), which means mutation to it is shared across users of 'elliptic' via the in-memory representation of those objects.

This is not generally a problem, for example, with `validate` it's a simple set, so the greatest risk is that it will be directly overwritten.

But in the case of `getX` and `getY`, both methods are overwritten with others that depend on the prior implementation as stored in `_get*`. If this happens twice, then the implementation of `_getX` is replaced with something that depends on a call to `_getX`, and the callers is stuck in an infinite loop.

bitcore-lib.js

@@ -2084,27 +2084,27 @@ Point.getN = function getN() {
   return new BN(ec.curve.n.toArray());
 };
 
-Point.prototype._getX = Point.prototype.getX;
+Point._getX = Point.prototype.getX;
 
 /**
  *
  * Will return the X coordinate of the Point
  *
  * @returns {BN} A BN instance of the X coordinate
  */
-Point.prototype.getX = function getX() {
+Point.getX = function getX() {
   return new BN(this._getX().toArray());
 };
 
-Point.prototype._getY = Point.prototype.getY;
+Point._getY = Point.prototype.getY;
 
 /**
  *
  * Will return the Y coordinate of the Point
  *
  * @returns {BN} A BN instance of the Y coordinate
  */
-Point.prototype.getY = function getY() {
+Point.getY = function getY() {
   return new BN(this._getY().toArray());
 };
 

lib/crypto/point.js

@@ -73,27 +73,27 @@ Point.getN = function getN() {
   return new BN(ec.curve.n.toArray());
 };
 
-Point.prototype._getX = Point.prototype.getX;
+Point._getX = Point.prototype.getX;
 
 /**
  *
  * Will return the X coordinate of the Point
  *
  * @returns {BN} A BN instance of the X coordinate
  */
-Point.prototype.getX = function getX() {
+Point.getX = function getX() {
   return new BN(this._getX().toArray());
 };
 
-Point.prototype._getY = Point.prototype.getY;
+Point._getY = Point.prototype.getY;
 
 /**
  *
  * Will return the Y coordinate of the Point
  *
  * @returns {BN} A BN instance of the Y coordinate
  */
-Point.prototype.getY = function getY() {
+Point.getY = function getY() {
   return new BN(this._getY().toArray());
 };