Fix File:copy FD leak, and add file-closes to some tests.

tests/standalone/io/file_invalid_arguments_test.dart

 // Copyright (c) 2013, 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.
 
 import "dart:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 void testReadInvalidArgs(arg) {
   String filename = getFilename("tests/vm/data/fixed_length_file");
   var file = (new File(filename)).openSync();
   Expect.throws(() => file.readSync(arg),
                 (e) => e is ArgumentError);
 
   Expect.throws(() => file.read(arg),
                 (e) => e is ArgumentError);
+  file.closeSync();
 }
 
 void testReadIntoInvalidArgs(buffer, start, end) {
   String filename = getFilename("tests/vm/data/fixed_length_file");
   var file = (new File(filename)).openSync();
   Expect.throws(() => file.readIntoSync(buffer, start, end),
                 (e) => e is ArgumentError);
 
   Expect.throws(() => file.readInto(buffer, start, end),
                 (e) => e is ArgumentError);
+  file.closeSync();
 }
 
 void testWriteByteInvalidArgs(value) {
   String filename = getFilename("tests/vm/data/fixed_length_file");
   var file = (new File("${filename}_out")).openSync(mode: FileMode.WRITE);
   Expect.throws(() => file.writeByteSync(value),
                 (e) => e is ArgumentError);
 
   Expect.throws(() => file.writeByte(value),
                 (e) => e is ArgumentError);
+  file.closeSync();
 }
 
 void testWriteFromInvalidArgs(buffer, start, end) {
   String filename = getFilename("tests/vm/data/fixed_length_file");
   var file = (new File("${filename}_out")).openSync(mode: FileMode.WRITE);
   Expect.throws(() => file.writeFromSync(buffer, start, end),
                 (e) => e is ArgumentError);
 
   Expect.throws(() => file.writeFrom(buffer, start, end),
                 (e) => e is ArgumentError);
+  file.closeSync();
 }
 
 void testWriteStringInvalidArgs(string, encoding) {
   String filename = getFilename("tests/vm/data/fixed_length_file");
   var file = new File("${filename}_out").openSync(mode: FileMode.WRITE);
   Expect.throws(() => file.writeStringSync(string, encoding: encoding),
                 (e) => e is ArgumentError);
 
   Expect.throws(() => file.writeString(string, encoding: encoding),
                 (e) => e is ArgumentError);
+  file.closeSync();
 }
 
 Future futureThrows(Future result) {
   return result.then((value) {
     throw new ExpectException(
         "futureThrows received $value instead of an exception");
     },
     onError: (_) => null
   );
 }
@@ skipping 33 matching lines @@
   testReadIntoInvalidArgs(12, 0, 1);
   testReadIntoInvalidArgs(new List(10), '0', 1);
   testReadIntoInvalidArgs(new List(10), 0, '1');
   testWriteByteInvalidArgs('asdf');
   testWriteFromInvalidArgs(12, 0, 1);
   testWriteFromInvalidArgs(new List(10), '0', 1);
   testWriteFromInvalidArgs(new List(10), 0, '1');
   testWriteStringInvalidArgs("Hello, world", 42);
   testFileSystemEntity();
 }