Per emerging standard in GNU programs and elsewhere.  Autoconf already
has support for specifying a home page, so we can just that.
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://www.postgresql.org/message-id/flat/8d389c5f-7fb5-8e48-9a4a-68cec44786fa%402ndquadrant.com