Make "native" not a keyword.

Make "native" not a keyword.

We now only recognize "native function" when it occurs in extension scripts
(parsing with a non-NULL extension), and only if there is no line-terminator
between "native" and "function" (so that it would otherwise be a Syntax Error).
Preparsing never recognizes native functions, which is acceptable since we
never preparse extension scripts (because we don't allow lazy functions
anyway).

BUG=v8:1097

Review URL: http://codereview.chromium.org/7206020

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8326 ce2b1a6d-e550-0410-aec6-3dcde31c8c00