Fix bug that could cause a string to be incorrectly tagged as an array index.

Fix bug that could cause a string to be incorrectly tagged as an array index. 
We should only mark a string as an array index if we can store the entire value 
of the number in the hash field. We sometimes failed to reject larger numbers.

Fixes http://code.google.com/p/v8/issues/detail?id=728

[Søren Thygesen Gjesse, 2010-06-02 09:27:03]

LGTM

http://codereview.chromium.org/2452007/diff/1/3
File test/cctest/test-strings.cc (right):

http://codereview.chromium.org/2452007/diff/1/3#newcode439
test/cctest/test-strings.cc:439: // We incorrectly allowed strings to be tagged
as array indices even if their
Maybe open a bug and refer to it here.