Log Message:
Changes 9.0.1:
* Use a separate interpreter for each calling SQL userid in PL/Perl and PL/Tcl
* Improve pg_get_expr() security fix so that the function can still be used on
  the output of a sub-select
* Fix incorrect placement of placeholder evaluation
* Fix join removal's handling of placeholder expressions
* Fix possible duplicate scans of UNION ALL member relations
* Prevent infinite loop in ProcessIncomingNotify() after unlistening
* Prevent show_session_authorization() from crashing within autovacuum
  processes
* Re-allow input of Julian dates prior to 0001-01-01 AD
* Make psql recognize "DISCARD ALL" as a command that should not be \ 
encased in
  a transaction block in autocommit-off mode
* Update build infrastructure and documentation to reflect the source code
  repository's move from CVS to Git