Rewrote sqimap_fread to make it work on PHP 4.3.2.

Rewrote sqimap_fread to make it work on PHP 4.3.2.
The fread behaviour was changed with as result that fread didn't return
when the requested buffersize was full but at a earlier stage, at the end of
a tcp packet.
From now on fread stops on: EOF, full buffer and in case of sockets at end
of packet if the imap server isn't providing the requested data quick
enough.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@5771 7612ce4b-ef26-0410-bec9-ea0150e637f0