A trailing backslash on the moodle data directory entry during configuration creates a bad config.php file

During the configuration process, if one enters a moodle data directory with a trailing backslash, this writes a bad config.php file and generates, to the user, a confusing error message. The trailing backslash escapes the closing single quote in php, which happens to be the last single quote, and php considers the file to end prematurely, etc.

Need to filter the entries in the configuration process...