another minor translator enhancement

[Hugh Hoover <heh>]

I fixed up the translator so it yield 'operator[]' instead of 'arrayFetch'
for a method named at:  I think this is more consistent with the translation
of at: and at:put: to [] and []=.

  I also did it because WordVector defines operator[] and I wanted a way to
generate it (to maintain the obsolete interface).

  Now, have you got any ideas on how to generate #ifdef's?