[PATCH] Sort contents entries in reference documentation

Hi,

While looking at the documentation on SELECT I noticed that the
entries in reference.sgml aren't sorted correctly -- psql \h does have
them in the correct order.

Attached a trivial patch to fix this.

In addition, reference.sgml doesn't have entries for TABLE or WITH
which should link to ref/select.sgml but I couldn't figure out how to
achieve this. psql \h does have this so the reference page probably
should too.

Cheers,

Colin