Recent overhaul of the Mozilla trunk has broken the patches.
Because bug #18574 has been WONTFIXED, I won't be fixing the patches
Please check out a version earlier than March 2007 if you wish
to build a MNG-capable browser using the patches available here.
Currently i am still able to build with MNG/JNG support, but i havent nuked my tree for a while. I have been fixing up the checkout conflicts as they happen, but if they have changed the trunk as much as you say, i may have to try a clean pull to get rid of the extra crap that shouldnt be there anymore.
your latest patch (1.9a3) seems to be reversed, as in it is removing MNG not adding it back in ;)
I don't actually know how to check out the earlier version. I tried
cvs co -D "2007-03-05 12:00" mozilla/client.mk
but it fails because modules.mk "is no longer pertinent".
If someone figures this out please post the solution here.