Although the `for..in` statement allows Expressions to define the
iterator, only an AssignmentExpression may occupy this position in the
`for..of` statement.

- Remove duplicate word
- Add missing license

The `negative` frontmatter tag expresses an expectation for the behavior
of the test file as a whole. The `assert.throws` helper function offers
more fine-grained control over expectations because it may be applied to
specific statements and expressions. This makes it preferable in cases
where it may be used (i.e. when the test body does not describe a syntax
error or early error).

Re-implement assertions for errors to use the `assert.throws` helper
function wherever possible.

- Add missing "var" declarations and noStrict flags
- Add strict mode tests for:
 - arguments-object/10.6-6-3 -> arguments-object/10.6-6-3-s
 - arguments-object/10.6-6-4 -> arguments-object/10.6-6-4-s
- Remove try-finally clean-up code
- Add strict mode compatible tests for eval-code/S10.4.2_A1.1_T*
  - No strict mode compatible files added for eval-code/S10.4.2_A1.2_T*, because it doesn't really make sense in this context.
  - (S10.4.2_A1.1 and S10.4.2_A1.2 should probably be removed, because the tested behaviour is not required by the spec.)
- Split S8.5_A10, S8.5_A4 and S8.1_A3 into declaration (both modes) and assignment tests (non-strict only)

Part of issue #35.

- Expand ambiguous assertion messages and assert execution paths more
  finely.
- Improve variable names in `for..of` tests
  While the object created by a GeneratorFunction may be considered an
  "iterable", it is being used as an iterator in these tests. Naming the
  variable according to the way it is used improves the readability of
  the test body.
- Add 'features' attribute to test frontmatter
- Move tests
- Introduce additional `for..of` control flow tests

These tests are derived from the following files within the Google V8 project:

    test/mjsunit/es6/regress/regress-2506.js
    test/mjsunit/es6/regress/regress-3426.js
    test/mjsunit/es6/regress/regress-3683.js