Fix 11.13.1-4-29gs.js incorrect comment explanation (master)

SyntaxError => TypeError for writing to a non-writeable field.

Fixes #372

Add tests for WeakMap

Improve coverage of SetIteratorPrototype

Move tests for the FunctionPrototype intrinsic

Re-organize class tests

Test262 maintains most tests for the FunctionPrototype intrinsic within
the `test/built-ins/Function/prototype/` directory. Two tests are
defined within the otherwise-empty `test/built-ins/intrinsics/`
directory; relocate them to the canonical directory for consistency and
discoverability.

The `test/language/class/` directory contains a small subset of
Test262's tests for ES2015 classes. The majority of tests for classes
are organized within `test/language/statements/class/`.

- Move the tests that rely on the ClassDeclaration syntactic form from
  `test/language/class/` to `test/language/statements/class/`.
- Move the test that relies on the ClassExpression syntactic form from
  `test/language/class/` to `test/language/expressions/class/`.

Clean-up test comments and remove invalid tests

Add test for built-in accessor properties names

Unicode escape identifiers

Re-organize generator tests

- Re-organize existing tests for identifiers
  Name files according to their content (not their ES5 ID). Move tests
  for IdentifierName and LabelIdentifier to more appropriate directories.
- Simplify and correct tests
  Instead of asserting successful runtime evaluation using `eval`, rely
  on the test runner's ability to detect syntax errors. Update the test
  bodies to test the grammar referenced by their ES5 ID and
  description--the IdentifierStart pattern.
- Use `negative` frontmatter to assert SyntaxErrors
- Remove redundant tests
- Use `assert.equal` helper function
- Add equivalent tests for literal unicode chars
- Add tests for variable-length unicode escape

The `test/language/generators/` directory contained a single file that
concerned generators derived both from syntactic form and from a
built-in function.

Refactor this test into two files and place each in the appropriate
directory.

- 15.10.2.15-3-1 and 15.10.2.15-3-2 are both invalid (U+002F (SOLIDUS) instead of U+005C (REVERSE SOLIDUS) was used to start an escape sequence).
- 15.10.4.1-2 and 15.10.2.2-1 are identical tests, delete the latter.
- Update tests to avoid using runTestCase() function.
- Update multiple test infos to point to correct algorithm step (CharacterRange step 6 instead of step 1).

Fix, update and improve coverage of MapIteratorPrototype

Formalize tests for built-in Promise methods 

Implement `raw` flag

Add tests for Map

Uniformly and exhaustively test the generic aspects of the static- and
instance Promise methods, including:

- function `length` properties
- function `name` properties
- method property descriptors

Some tests involving the directive prologue are invalidated by source
text transformations that insert executable code in the beginning of the
script. Implement a `raw` flag that allows these tests to opt-out of
this transformation. Update the relevant tests to use this flag (and
remove references to globals only available when code is injected).

Update the Python runner accordingly:

- Do not run tests marked as "raw" in strict mode
- Reject invalid test configurations

Update the browser runner accordingly:

- Do not modify the script body of tests marked as "raw"