Update .htaccess

Delete a bugfix for PHP4, because the current version requires at least PHP 5.2.1. The case thus never occurs.
Update styles.css

added support for required field (HTML5)
added border:none; for logos and delete deprecated border="0" html attribute
Update html.php

added required attribute to allowed list for input fields
Update login.html

deleted deprecated border="0" Attribute and use css instead
Update header.html

deleted old border="0" attribute and use css instead
Update rcmail_output_html.php

added required Attribute to Login fields
Avoid session timeouts with memcache backend as proposed by D. Carter via users mailing list
Update mail.html

deleted deprecated frameborder Attribute and use css instead
wrong closing DIV tag
Update addressbook.html

deleted deprecated frameborder attribute and use css instead
Update settings.html

deleted deprecated frameborder attribute and use css instead
Update func.inc

added missing ID for label
replaces smart quotes with regular quotes. Fixes improper doctype declarations in html emails
Fix priority selector when open in new window (#1489257)
Better check for priority header
Fix parsing of links with ... in URL (#1489192)
Updated Changelog
Fix identity-selection using Return-Path headers (#1489241)
Updated changelog
Update mail.html

added old frameborder Attribute for IE7 and IE8
Update addressbook.html

added old frameborder Attribute for IE7 and IE8