Fix #12366: file_api uses old style calls to db_get_table

file_api uses some old style calls to db_get_table(..), similar to:
db_get_table( 'mantis_bug_file_table' )

Instead of the newer argument format:
db_get_table( 'bug_file' );

Signed-off-by: David Hicks <hickseydr@optusnet.com.au>

core/file_api.php

@@ -891,13 +891,13 @@ function file_get_content( $p_file_id, $p_type = 'bug' ) {
 	$query = '';
 	switch ( $p_type ) {
 		case 'bug':
-			$t_bug_file_table = db_get_table( 'mantis_bug_file_table' );
+			$t_bug_file_table = db_get_table( 'bug_file' );
 			$query = "SELECT *
 				FROM $t_bug_file_table
 				WHERE id=" . db_param();
 			break;
 		case 'doc':
-			$t_project_file_table = db_get_table( 'mantis_project_file_table' );
+			$t_project_file_table = db_get_table( 'project_file' );
 			$query = "SELECT *
 				FROM $t_project_file_table
 				WHERE id=" . db_param();