Keyword list sanity check

I wrote a little perl script to perform a basic sanity check to keywords
in gram.y and kwlist.h. It checks that all lists are in alphabetical
order, all keywords present in gram.y are listed in kwlist.h in the
right category, and conversely that all keywords listed in kwlist.h are
listed in gram.y.

It found one minor issue already:

$ perl src/tools/check_keywords.pl
'SCHEMA' after 'SERVER' in unreserved_keyword list is misplaced

SERVER is not in the right place in gram.y, it should go between
SERIALIZABLE and SERVER. I'll fix that.

I'll put this into src/tools. It's heavily dependent on the format of
the lists in gram.y and kwlist.h but if it bitrots due to changes in
those files, we can either fix it or just remove it if it's not deemed
useful anymore.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com