PostgreSQL: Support table prefixes

PostgreSQL: Support table prefixes

PostgreSQL is usually not used with table name prefixes,
and some of the PostgreSQL-specific code took the
shortcut of not dealing with prefixes.  However, the PHPUnit
tests do force a prefix to be used, exposing this limitation.

Make PostgreSQL code add the prefix to table names being used
in FOR UPDATE OF clause.

This fixes 13 of the 17 PostgreSQL unit tests errors against
git HEAD:

EditPageTest::testAutoMerge with data set #1 ('Elmo', 'one
EditPageTest::testAutoMerge with data set #2 ('Elmo', 'Intro
EditPageTest::testAutoMerge with data set #3 ('Adam', 'one
EditPageTest::testAutoMerge with data set #4 ('Adam', 'one
EditPageTest::testAutoMerge with data set #5 ('Adam', 'Intro
EditPageTest::testAutoMerge with data set #6 ('Berta', 'one
EditPageTest::testAutoMerge with data set #7 ('Berta', 'one
EditPageTest::testAutoMerge with data set #8 ('Berta', 'Intro
WikiPageTest::testDoEdit
WikiPageTest::testDoEditContent
WikiPageTest::testDoRollback
WikiPageTest::testDoRollbackFailureSameContent
WikiPageTest::testExists

The change also applies to 1.22.6 and fixes several unit tests
errors there.

Change-Id: I054690f49e250cadd2dc2a6d9e20dea879d896b6