Start work on lexical embedding with closure-a-like object.

Unfinished.
Merge branch 'pypy_bridge' into pypy_bridge_embed_py_func_local
Fix whitespace.
Initial implementation of embed_py_func_lexical().
Replace old embed_py_func() with embed_py_func_lexical()
Remove old EmbeddedPyFunc data structure.
Rename data structures and support funcs.
Test for a bug: Python can call PHP builtins but not vica-versa.
Add immutable fields.
Whitespace.
Create callable directly where possible.

Remove misleading comment.
Unbreak existing argument passing semantics.

Uses a is_py_call() method on functions.
Undo errorneous change.