[imp] Notices after upgrade to php 4.4.0.

[Thomas Sjolshagen]

After upgrading to php 4.4.0, I'm getting the following warnings. (Also, there's
a similar warning/notice for PEAR::Log in /usr/lib/php/Log.php, but that's OT
for this list).

Logging in:
-----------

Notice: Only variable references should be returned by reference in
/local/horde/lib/Horde/Notification.php on line 98


Then when reading a message:
-----------------------------

Notice: Only variable references should be returned by reference in
/local/horde/lib/Horde/Notification.php on line 98

Notice: Only variables should be assigned by reference in
/local/horde/lib/Horde/MIME/Contents.php on line 1146

Notice: Only variable references should be returned by reference in
/local/horde/lib/Horde/MIME/Contents.php on line 1146

Notice: Only variables should be assigned by reference in
/local/horde/lib/Horde/MIME/Contents.php on line 647