fix spelling in core libraries

sdk/lib/core/date_time.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.core;
 
 /**
  * An instant in time, such as July 20, 1969, 8:18pm GMT.
  *
  * Create a DateTime object by using one of the constructors
@@ skipping 16 matching lines @@
  *
  * You can use properties to get
  * the individual units of a DateTime object.
  *
  *     assert(berlinWallFell.month == 11);
  *     assert(moonLanding.hour == 20);
  *
  * For convenience and readability,
  * the DateTime class provides a constant for each day and month
  * name—for example, [AUGUST] and [FRIDAY].
- * You can use these constants to improve code readibility:
+ * You can use these constants to improve code readability:
  *
  *     DateTime berlinWallFell = new DateTime(1989, DateTime.NOVEMBER, 9);
  *     assert(berlinWallFell.weekday == DateTime.THURSDAY);
  *
  * Day and month values begin at 1, and the week starts on Monday.
  * That is, the constants [JANUARY] and [MONDAY] are both 1.
  *
  * ## Working with UTC and local time
  *
  * A DateTime object is in the local time zone
@@ skipping 163 matching lines @@
    *   then optionally a two digit seconds value, and
    *   then optionally a '.' followed by a one-to-six digit second fraction.
    *   The minutes and seconds may be separated from the previous parts by a
    *   ':'.
    *   Examples: "12", "12:30:24.124", "123010.50".
    * * An optional time-zone offset part,
    *   possibly separated from the previous by a space.
    *   The time zone is either 'z' or 'Z', or it is a signed two digit hour
    *   part and an optional two digit minute part. The sign must be either
    *   "+" or "-", and can not be omitted.
-   *   The minutes may be separted from the hours by a ':'.
+   *   The minutes may be separated from the hours by a ':'.
    *   Examples: "Z", "-10", "01:30", "1130".
    *
    * This includes the output of both [toString] and [toIso8601String], which
    * will be parsed back into a `DateTime` object with the same time as the
    * original.
    *
    * The result is always in either local time or UTC.
    * If a time zone offset other than UTC is specified,
    * the time is converted to the equivalent UTC time.
    *
@@ skipping 535 matching lines @@
    * In accordance with ISO 8601
    * a week starts with Monday, which has the value 1.
    *
    *     DateTime moonLanding = DateTime.parse("1969-07-20 20:18:00");
    *     assert(moonLanding.weekday == 7);
    *     assert(moonLanding.weekday == DateTime.SUNDAY);
    *
    */
   external int get weekday;
 }