Proposed fix for #773

Split up check_setup.php into two files. The new file check_essentials.php takes care of stuff like the PHP version and is executed before the config files are included which are needed by check_setup. This patch addresses issue #773
Yes. I've tested it with mysql and sqlite. Did behave as it should. The only time this may be problematic is if another file based database would be added. Then this would need to be extended by another statement or converted into a regex.