Update pub to use new import syntax.

utils/pub/exit_codes.dart

 // Copyright (c) 2012, 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.
 
 /// Exit code constants. From [the BSD sysexits manpage][manpage]. Not every
 /// constant here is used, even though some of the unused ones may be
 /// appropriate for errors encountered by pub.
 ///
 /// [manpage]: http://www.freebsd.org/cgi/man.cgi?query=sysexits
-#library('exit_codes');
+library exit_codes;
 
 /// The command was used incorrectly.
 final USAGE = 64;
 
 /// The input data was incorrect.
 final DATA = 65;
 
 /// An input file did not exist or was unreadable.
 final NO_INPUT = 66;
 
@@ skipping 25 matching lines @@
 final TEMP_FAIL = 75;
 
 /// The remote system returned something invalid during a protocol exchange.
 final PROTOCOL = 76;
 
 /// The user did not have sufficient permissions.
 final NO_PERM = 77;
 
 /// Something was unconfigured or mis-configured.
 final CONFIG = 78;