Multisite fixes for Relevanssi and WP 5.1

relevanssi_multisite_fixes.php

<?php

// In /lib/install.php, replace the relevanssi_new_blog() function with this:

function relevanssi_new_blog( $blog ) {
	if ( is_int( $blog ) ) {
		$blog_id = $blog;
	} else {
		$blog_id = $blog->id;
	}
	if ( is_plugin_active_for_network( 'relevanssi-premium/relevanssi.php' ) || is_plugin_active_for_network( 'relevanssi/relevanssi.php' ) ) {
		switch_to_blog( $blog_id );
		_relevanssi_install();
		restore_current_blog();
	}
}

/*

In relevanssi.php, remove the line:

add_action( 'wpmu_new_blog', 'relevanssi_new_blog', 10, 1 );

and add this:
*/

global $wp_version;
if ( version_compare( $wp_version, '5.1', '>=' ) ) {
	add_action( 'wp_insert_site', 'relevanssi_new_blog', 10, 1 );
} else {
	add_action( 'wpmu_new_blog', 'relevanssi_new_blog', 10, 1 );
}