From: Jason Childs <oblivian@users.sourceforge.net>
Date: Tue, 11 Aug 2009 23:55:20 -0400
Subject: [PATCH] Color transparency support

Add alpha to Color structure to support transparency. This change tries
to be a uninstrusive as possible, any and all references to Color have
either been upgraded to read/write the new alpha parameter or they
default to 1.0 to retain the existing functionality.
If the plugin/importer/exporter does not support transparency, it will
render the same as before.  The cairo renderer has been updated to use
alpha and the dia file format has been extended to understand both the
new alpha value and support older files that don't have alpha for color
values.