Fixed an error in the date and time parser's handling of time zones.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=140400905

library/src/androidTest/java/com/google/android/exoplayer2/util/UtilTest.java

@@ -142,6 +142,8 @@ public class UtilTest extends TestCase {
   public void testParseXsDateTime() throws Exception {
     assertEquals(1403219262000L, Util.parseXsDateTime("2014-06-19T23:07:42"));
     assertEquals(1407322800000L, Util.parseXsDateTime("2014-08-06T11:00:00Z"));
+    assertEquals(1411161535000L, Util.parseXsDateTime("2014-09-19T13:18:55-08:00"));
+    assertEquals(1411161535000L, Util.parseXsDateTime("2014-09-19T13:18:55-0800"));
   }
 
   public void testUnescapeInvalidFileName() {

library/src/main/java/com/google/android/exoplayer2/util/Util.java

@@ -95,7 +95,7 @@ public final class Util {
   private static final Pattern XS_DATE_TIME_PATTERN = Pattern.compile(
       "(\\d\\d\\d\\d)\\-(\\d\\d)\\-(\\d\\d)[Tt]"
       + "(\\d\\d):(\\d\\d):(\\d\\d)(\\.(\\d+))?"
-      + "([Zz]|((\\+|\\-)(\\d\\d):(\\d\\d)))?");
+      + "([Zz]|((\\+|\\-)(\\d\\d):?(\\d\\d)))?");
   private static final Pattern XS_DURATION_PATTERN =
       Pattern.compile("^(-)?P(([0-9]*)Y)?(([0-9]*)M)?(([0-9]*)D)?"
           + "(T(([0-9]*)H)?(([0-9]*)M)?(([0-9.]*)S)?)?$");