Add safe_mode notes in configtest; it might be nice to expand these to do more automa...

Add safe_mode notes in configtest; it might be nice to expand these to do more automated checks (for example, that the webserver has access to the data dir or attachment dir, or that DB.php is accessible, although that is done elsewhere herein)

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@12716 7612ce4b-ef26-0410-bec9-ea0150e637f0