Moving the GUI to Savannah

[Jordi Gutiérrez Hermoso]

Although I have been wanting to wait until the GUI's build system was
integrated with Octave's before pushing it to Savannah, I think it's
better if we just push the GUI to Savannah right now and work on it
there. Talked about it with jwe in #octave, and he seems to be ok with
this idea.

However, because the GUI isn't quite ready, I will put it on a
separate head in Savannah *but* with an hg bookmark. It will not be
part of the 3.6 release, but hopefully we can release the GUI for the
release after 3.6. I will create two bookmarks, one called "dev" that
points to the current ordinary default branch in Savannah, and one
called "gui" that points to the current development branch that I had
in bitbucket. Here is some documentation about bookmarks:

    http://mercurial.selenic.com/wiki/BookmarksExtension

If you are using hg 1.8 or later, next time you pull from Savannah
after I push the GUI there you will possibly have one more head, for
the GUI.

If you are using an earlier version of hg, you will have to enable the
bookmark extension in your .hgrc:

    [extensions]
    hgext.bookmarks =

Basically, there are now two heads on the default branch, with
bookmarks to distinguish them. The point of the bookmarks is that the
GUI separate development is supposed to be a temporary thing, so once
we integrate the GUI with the build system, we will merge the GUI head
onto the dev head and remove the bookmarks. It's almost the same as
having a separate branch of development, but it's more lightweight in
the sense that the GUI branch won't exist as a separate branch in
history forever. Rather, it's a new head in the default branch, with a
little bookmark that says where you are. When you commit on a revision
that has the bookmark, the bookmark will now move to your new commit.

I have been regularly merging the GUI head in Bitbucket with the
Savannah default branch, so roughly stable < Savannah < GUI by order
of inclusion. Merging works the same, you do "hg up gui", you say "hg
merge dev", you commit the merge, and then the gui head will have
everything that is in the dev head. When we're ready to get rid of the
bookmarks, we do "hg up dev && hg merge gui" and then the dev head
will have everything that the gui head had.

I want to make sure everyone understands what the bookmarks are before
I push them to Savannah. If something isn't clear, ask now.

- Jordi G. H.