buffer: fix usage of kMaxLength

Starting in V8 v4.3 the maximum array index of a typed array is the same
as the largest Smi supported on a given architecture. To compensate for
these differences export kMaxLength from the buffer module with the
correct size for the given architecture.

PR-URL: https://github.com/nodejs/io.js/pull/2003


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>