Load xmledit plugin, even if $VIMRUNTIME/ftplugin/xml.vim or html.vim load first.

Hi, 
Since I use neobundle to manage plugins, the load path of xmledit plugin should be after $VIMRUNTIME/ftplugin. I found that if xml.vim and html.vim located in $VIMRUNTIME/ftplugin is loaded, the xmledit plugin must not be loaed. It seems that xmledit use the same buffer variable -- 'b:did_ftplugin'  to avoid plugin loaded again. So I add the patch to load xmledit plugin, even if $VIMRUNTIME/ftplugin/xml.vim or html.vim load first.

Thanks & Best Regards,
Liang Feng