Often on the mailing list there is confusion about NOT_ANALYZED.
Besides being useless (Just use KeywordAnalyzer instead), people trip up on this
not being consistent at query time (you really need to configure KeywordAnalyzer for the field
on your PerFieldAnalyzerWrapper so it will do the same thing at query time... oh wait
once you've done that, you dont need NOT_ANALYZED).
So I think StringField is a trap too for the same reasons, just under a
different name, lets remove it.