This enables factory functions to be registered for API modules,
in addition to the module class itself. This allows modules to
use proper dependency injection via the modules constructor.
Example:
$wgAPIModules['foo'] = array(
'class' => 'ApiFoo',
'factory' => function( $main, $action ) { ... }
)
Change-Id: Ieb85493a7765f466317f5fa74b0b0e262220deab
