NLS changes

Patchers,

Here is a patch related to NLS that

- adds .y files to gettext-files in backend/nls.mk.  gram.y contains
  several translatable messages that are not catched by update-po unless
  the gram.c file is generated.  I don't know if this is desirable but I
  think it's better to have to gram.y file processed.
  Maybe this part of the patch could be left out (it's the first,
  trivial chunk).

- makes more translator-friendly the messages in gram.y, because a lot
  of them are only a keyword away of being equal.  This avoids having
  the translator process the same thing several times.

- adds a couple of comments for the translator (I had to peek at the
  source code to see what the %s was about, so I guess this is needed).


Also, I've noted that psql's \h messages are not translatable.  Is there
a way to make them so?

I have the backend messages almost done:

$ LANG= msgfmt -c -v es.po
1757 translated messages, 29 untranslated messages.

I'll submit after I resolve a couple of translations that are not clear.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"La victoria es para quien se atreve a estar solo"