Use Node.js crypto ripemd160 hash if available.

lib/crypto/hash.js

@@ -29,10 +29,19 @@ Hash.sha256sha256 = function(buf) {
 
 Hash.ripemd160 = function(buf) {
   $.checkArgument(BufferUtil.isBuffer(buf));
-  var hash = (new hashjs.ripemd160()).update(buf).digest();
-  return new Buffer(hash);
+  return crypto.createHash('ripemd160').update(buf).digest();
 };
 
+// Node.js crypto ripemd160 hashes are not supported in a browser
+// We'll replace with a (slower) version that does.
+if (global.window) {
+  Hash.ripemd160 = function(buf) {
+    $.checkArgument(BufferUtil.isBuffer(buf));
+    var hash = (new hashjs.ripemd160()).update(buf).digest();
+    return new Buffer(hash);
+  };
+}
+
 Hash.sha256ripemd160 = function(buf) {
   $.checkArgument(BufferUtil.isBuffer(buf));
   return Hash.ripemd160(Hash.sha256(buf));