simplify computing of runtime file locations

bin/devc.dart

 #!/usr/bin/env dart
 // Copyright (c) 2015, 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.
 
 /// Command line tool to run the checker on a Dart program.
-library dev_compiler.bin.checker;
+library dev_compiler.bin.devc;
 
 import 'dart:io';
 
 import 'package:dev_compiler/devc.dart';
 import 'package:dev_compiler/src/options.dart';
 
 void _showUsageAndExit() {
   print('usage: dartdevc [<options>] <file.dart>\n');
   print('<file.dart> is a single Dart file to process.\n');
   print('<options> include:\n');
@@ skipping 19 matching lines @@
 
   setupLogger(options.logLevel, print);
 
   if (options.serverMode) {
     new CompilerServer(options).start();
   } else {
     var result = new Compiler(options).run();
     exit(result.failure ? 1 : 0);
   }
 }