Make insertSelect() do two separate queries in non-CLI mode

Make insertSelect() do two separate queries in non-CLI mode

This avoids slave lag and makes query time account easier.
It also avoids table-level autoinc locking and slave drift
with statement-based replication in some setups.

Also refactored the use of $wgCommandLine mode in
DatabaseBase slightly, so that it can be injected.

Change-Id: I2dba6024ecf32c9ee24a3080cce3b02568c1458b