Constructs the (generally cyclic) graph of module instance objects
and populates their exports. Any exports other than nested modules
are currently set to 'undefined' (but already present as properties).

Details:
- Added new type JSModule for instance objects: a JSObject carrying a context.
- Statically allocate instance objects for all module literals (in parser 8-}).
- Extend interfaces to record and unify concrete instance objects,
  and to support iteration over members.
- Introduce new runtime function for pushing module contexts.
- Generate code for allocating, initializing, and setting module contexts,
  and for populating instance objects from module literals.
  Currently, all non-module exports are still initialized with 'undefined'.
- Module aliases are resolved statically, so no special code is required.
- Make sure that code containing module constructs is never optimized
  (macrofy AST node construction flag setting while we're at it).
- Add test case checking linkage.

Baseline: http://codereview.chromium.org/9722043/

R=svenpanne@chromium.org,mstarzinger@chromium.org
BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/9844002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11336 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

All module expressions, and all variables that might refer to modules,
are assigned interfaces (module types) that are resolved using
unification. This is necessary to deal with the highly recursive
nature of ES6 modules, which does not allow any kind of bottom-up
strategy for resolving module names and paths.

Error messages are rudimental right now. Probably need to track
more information to make them nicer.

R=svenpanne@chromium.org
BUG=v8:1569
TEST=

Review URL: https://chromiumcodereview.appspot.com/9615009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10966 ce2b1a6d-e550-0410-aec6-3dcde31c8c00