p5-DBD-postgresql: updated to 3.9.1

Version 3.9.1:
Bugfix for pg_error_field: make sure we do not feed null to newSVpv,
handle older versions of Postgres better.

Version 3.9.0:
- ShowErrorStatement works for "quickexec" do() calls
- Add :pg_limits to add constants such as PG_MAX_SMALLINT
- Add $dbh->pg_error_field() function
- Fix failing tests due to incorrect 'initdb' check

Version 3.8.1:
- Fix encoding of SQL_VARBINARY type in $dbh->quote() function
- Fix encoding in $dbh->do() function
- Fix E'' string escape handling on architectures with unsigned chars
- Minor fix to allow DBD::Pg to connect to PGbouncer's internal 'pgbouncer' database.
- Fix so table_info test works on non-empty databases

Version 3.8.0:
- Increase minimum supported PostgreSQL version to 8.0
- Add support for foreign tables in table_info() and column_info()
- Return the current database name as TABLE_CAT in info methods
- Handle backslash-escaped quotes in E'' strings
- Fix typo in Makefile.PL
- Fix parsing of PostgreSQL versions >= 10 on Debian/Ubuntu
- Fix client_min_messages=FATAL test when PostgreSQL caps it to ERROR
- Fix ->ping error detection on PostgreSQL 12
- Adjust tests for new pg_ctl output
- Adjust tests for removal of WITH OIDS in PostgreSQL 12
- Fix support for PostgreSQL versions back to 8.0
- Remove usage of deprecated pg_attrdef.adsrc and pg_constraint.consrc columns
- Fix typo in pg_placeholder_colons example
- Support GENERATED ... AS IDENTITY columns in last_insert_id()


(adam)