Fix usage of $wgDebugDumpSql

- In DatabaseMssql, use $this->debug() instead of $wgDebugDumpSql
  so that it takes into account the DBO_DEBUG flag
- Use the same construction to set the DBO_DEBUG flag in
  LBFactorySimple::newMainLB() as for the other flags so that
  it is easier to read the code

Change-Id: Ie775cdb3677739a97e0d64dabbf80fc685149337
Merge "Fix usage of $wgDebugDumpSql"