Patch for bookmark properties (t6)

[Peter Harvey <peter a harvey gmail com>]

Hi all,

Yet another patch for the bookmark properties window. This one adds a
warning message in the dialog if you enter an address that is already
bookmarked (check out the screenshot). Including this patch would remove
the "Duplicate bookmark" dialog that appears when you select "Add
Bookmark".

  http://home.exetel.com.au/harvey/epiphany/t6.patch
  http://home.exetel.com.au/harvey/epiphany/t6.png

I also need feedback from people on the topic list combobox. Should we
remove it? Do people still want the flat list? Is anyone having trouble
with having topics arranged by Selection/Subtopics/Others?

Thanks,
Peter.