Made parser not accept unicode escapes inside "native" when used as a keyword.

Made parser not accept unicode escapes inside "native" when used as a keyword.

This is a regression relative to the original behavior, when "native" was a keyword,
since keywords cannot contain esacpes.

Added tests for escapes and for not allowing line-terminators betwen "native" and "function".

Committed: http://code.google.com/p/v8/source/detail?r=8327

[Lasse Reichstein, 2011-06-20 11:11:25]

I remembered that identifiers can contain escapes, so we suddently accepted
"nativ\u0065" where we didn't before.

[Mads Ager (chromium), 2011-06-20 11:28:32]

LGTM