WYSIWYG under IE6 or Opera use uppercase to put IMG tag

Under my Windows XP, FCKeditor or Tinymce under IE6 or Opera, put a img tag with upercase
i.e.

<IMG style="WIDTH: 487px; HEIGHT: 144px ...

Problem exist because regular expression in the module is case sensitive.

This patch, resolve the problem (add case insensitive to the preg expression).

Tested on IE 6 and Opera.

btw. great module

-- sorry to double post in two isues, this was my first time to create patch:)