Html part duplicated in tinymail-gtkhtml

[Yang Hong <hongyang redflag-linux com>]

Hi, all

A html format email always comes with tow part, one in text/plain and
one in text/html:

{{{
------=_Part_186714_7571302.1231323028616
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

abc.com

------=_Part_186714_7571302.1231323028616
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

<a href="http://abc.com";>abc.com</a><br>

------=_Part_186714_7571302.1231323028616--
}}}

Currently, tinymail treats them as tow different part, and render it
separate in a gtk-mime-part-view and a gtk-html-mime-part-view, that is
strange from a user point view.

I think there should be an advanced tny-mime-part that contain both plan
and html format content in one part, and tny-mime-part-view also should
be improved to handle it: if there is html enabled view (such as
gtk-html-mime-part-view), then render the html part for user, if not,
render the plain part for user. 

Any comments?

BR

YangH