libpq++ fixes

This patch fixes a few minor problems with libpq++: remove the deprecated
PQExec(" ") in the wrapper around PQnotifies(), fix the Makefile for
the examples so that they will actually compile properly (with the
exception of #5, which depends on internal headers), make a minor change
to libpq++.h so that "make examples" now works on my machine, update
some documentation, fix some grammatical problems, and remove some of
the more hideous comments.

I plan on doing some more work on libpq++ in the future -- this patch just
consists of the necessary code to get the examples to compile on my machine,
plus corrections for any of the minor things I noticed on the way through.

Cheers,

Neil

--
Neil Conway <neilconway(at)rogers(dot)com>
PGP Key ID: DB3C29FC