[patch] Connect to old servers

Hi, thank you for this great software!

I'm not implying that support for old servers should be added or
announced, of course. But in my organization we are doomed to keep
some legacy servers (for now), certainly not something we are proud
of. When attempting to connect to those servers I get an error stating
that the configuration parameter "bytea_output" doesn't exist and
connection is then closed. You can figure how *old* I'm talking about
now.

So, instead of using the "SET configuration_parameter = value" I
changed it to "UPDATE pg_settings ..." (which is valid according to
the docs) to make it silently not set that parameter if it's not found
in the server. I also have some v11 clusters and can confirm using
"SHOW bytea_output" that it's still correctly set to "escape". But if
I access the same cluster from within "psql" program I get "hex".

Thank you very much.