Make native syntax an early error in the preparser.

Make native syntax an early error in the preparser.

Previously the preparser always accepted natives syntax and let the
real parser throw the syntax error. In ES5, it should be an early error,
so the preparser must catch the error.
The perparser library does not expose parsing for natives syntax, it's
only used internally.

Review URL: http://codereview.chromium.org/8306024

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@9660 ce2b1a6d-e550-0410-aec6-3dcde31c8c00