Date Parser: Improve timezone handling

- Handle special case when target date and today date are in different
  DST rules;

Fixes globalizejs#689

src/date/parse.js

@@ -227,7 +227,7 @@ return function( value, tokens, properties ) {
 			case "O":
 			case "X":
 			case "x":
-				timezoneOffset = token.value - date.getTimezoneOffset();
+				timezoneOffset = token.value;
 				break;
 		}
 
@@ -271,8 +271,8 @@ return function( value, tokens, properties ) {
 		date.setHours( date.getHours() + 12 );
 	}
 
-	if ( timezoneOffset ) {
-		date.setMinutes( date.getMinutes() + timezoneOffset );
+	if ( timezoneOffset !== undefined ) {
+		date.setMinutes( date.getMinutes() + timezoneOffset - date.getTimezoneOffset() );
 	}
 
 	// Truncate date at the most precise unit defined. Eg.

test/functional/date/parse-date.js

@@ -160,6 +160,8 @@ QUnit.test( "should parse raw pattern", function( assert ) {
 });
 
 QUnit.test( "should parse a formatted date (reverse operation test)", function( assert ) {
+	var OrigDate;
+
 	extraSetup();
 
 	ar = Globalize( "ar" );
@@ -168,6 +170,18 @@ QUnit.test( "should parse a formatted date (reverse operation test)", function(
 	date = startOf( date, "minute" );
 	assert.deepEqual( Globalize.parseDate( Globalize.formatDate( date, { datetime: "full" } ), { datetime: "full" } ), date );
 	assert.deepEqual( ar.parseDate( ar.formatDate( date, { datetime: "full" } ), { datetime: "full" } ), date );
+
+	// Test #689 - special test when target date and today are in different DST rules.
+	// Note it was arbitrarily chosen O, other timezone patterns are supposed to pass too.
+	// date1 = a DST date (or vice-versa depending on the running environment).
+	// FakeDate.today = a standard time date (or vice-versa depending on the running environment).
+	/* globals Date:true */
+	OrigDate = Date;
+	Date = util.FakeDate;
+	date = new Date( 2017, 6, 1, 12, 0 );
+	util.FakeDate.today = new Date( 2017, 0, 1 );
+	assert.deepEqual( Globalize.parseDate( Globalize.formatDate( date, { datetime: "full" } ), { datetime: "full" } ), date );
+	Date = OrigDate;
 });
 
 });