MS Exch can be set up that users have to use DOMAIN/username/mailbox

to log in. We need to strip these chars before creating the prefs
file, because of course a slash in the name gives problems.

It may be possible to strip out other 'illegal' chars here aswell.
Closes (#745814).

functions/prefs.php

@@ -51,7 +51,8 @@ function getHashedFile($username, $dir, $datafile, $hash_search = true) {
     /* First, get and make sure the full hash directory exists. */
     $real_hash_dir = getHashedDir($username, $dir, $hash_dirs);
 
-    /* Set the value of our real data file. */
+    /* Set the value of our real data file, after we've removed unwanted characters. */
+    $datafile = str_replace('/', '_', $datafile);
     $result = "$real_hash_dir/$datafile";
 
     /* Check for this file in the real hash directory. */