Handle PostgreSQL transaction errors and improve schema detection
* Introduce $wgDebugDBTransactions facility to help
figure out what's going on with transactions.
Currently PostgreSQL only.
PostgresTransactionState can be easily be made more general
to trace all sorts of state machinery.
* Improve r113408: we don't need to full reconnect on error,
rollback is enough.
Rolling back breaks search_path, as PostgreSQL
can manage sessions settings under transaction therefore
we need to improve schema sniffing introduced in r82674
* Introduce few schema handling functions. This could
probably be generalized for other databases like DB2 and Oracle.
* Fix bug 15816 - Add a switch for SETting the search_path
We try to avoid touching search_path at all unless
really necessary. Even in this case we append MediaWiki
core schema to the front of the list.
* No longer add $wgDBmwschema to PostgreSQL role search_path
in the installer. This is no longer necessary as
setting schema on connect should ReallyWorkNow(tm).
* Get rid as much as possible of $wgDBmwschema and
bring us one step closer to fix bug 16794 (wgSharedDB
support).
All references to core MediaWiki schema in PostgreSQL
specific code should now use Database::getCoreSchema()
unless we know what we are doing.
Followup-To: r113408 r82674