pg_autovacuum update

This patch updates pg_autovacuum in several ways:
* A few bug fixes
* fixes solaris compile and crash issue
* decouple vacuum analyze and analyze thresholds
* detach from tty (dameonize)
* improved logging layout
* more conservative default configuration
* improved, expanded and updated README

please apply and 1st convenience, or before code freeze which ever comes
first :-)

At this point I think I have brought pg_autovacuum and its client side
design as far as I think it should go.  It works, keeping file sizes in
check, helps performance and give the administrator a fair amount
flexibility in configuring it.

Next up is to do the FSM based design that is integrated into the back
end.

Matthew

p.s. Thanks to Christopher Browne for his help.