client-side AUTOCOMMIT mode now: '\set AUTOCOMMIT off' supports
SQL-spec commit behavior.  Get rid of LO_TRANSACTION hack --- the
LO operations just work now, using libpq's ability to track the
transaction status.  Add a VERBOSE variable to control verboseness
of error message display, and add a %T prompt-string code to show
current transaction-block status.  Superuser state display in the
prompt string correctly follows SET SESSION AUTHORIZATION commands.
Control-C works to get out of COPY IN state.