Update source file headers not to point to LICENSE.txt

[tdi]

Now, every source file points to license in LICENSE.txt. This prevents using files from libstrophe outside the libstrophe. My suggestion is to change this to put there a whole LICENSE.txt text in every file.

Example (was):

 /* handler.c
 ** strophe XMPP client library -- event handler management
 **
 ** Copyright (C) 2005-2009 Collecta, Inc. 
 **
 **  This software is provided AS-IS with no warranty, either express
 **  or implied.
 **
 **  This software is distributed under license and may not be copied,
 **  modified or distributed except as expressly authorized under the
 **  terms of the license contained in the file LICENSE.txt in this
 **  distribution.
 */

To:

 /* handler.c
 ** strophe XMPP client library -- event handler management
 **
 ** Copyright (C) 2005-2009 Collecta, Inc. 
 **
 **  This software is provided AS-IS with no warranty, either express
 **  or implied.
 **
 ** This program is dual licensed under the MIT and GPLv3 licenses.
 */

[tdi]

When you cope with sha problems and the repository is so-so stable I can rewrite the headers.