Add support for the package: directive in Frog and dart2js.

frog/reader.dart

Index: frog/reader.dart
diff --git a/frog/reader.dart b/frog/reader.dart
index 222fca254e6ecd58b645dc082dd348d2a0a4c699..2f2117909806c09449c439007b568b8c3c53cdbb 100644
--- a/frog/reader.dart
+++ b/frog/reader.dart
@@ -44,7 +44,14 @@ class LibraryReader {
   }
 
   SourceFile readFile(String fullname) {

[Bob Nystrom, 2012/04/09 23:54:08]

Should be "fullName".

[nweiz, 2012/04/10 00:16:31]

Done.

-    var filename = _specialLibs[fullname];
+    String filename;
+    if (fullname.startsWith('package:')) {
+      filename = joinPaths(dirname(options.dartScript),
+          joinPaths('packages', fullname.substring('package:'.length)));
+    } else {
+      filename = _specialLibs[fullname];
+    }
+
     if (filename == null) {
       filename = fullname;
     }