Please test the Explorer 1.0 branch - RC2 pending

[Ian Clatworthy]

Testing of the first release candidate on Windows revealed that the
tree-style toolbox was completely broken so I've replaced it with a
tab-style one on all platforms. (The tree-style toolbox is still
available as a preference for non-Windows users.) This is a large change
so I'm going to release a second release candidate as soon as I get some
confirmation the latest code looks OK everywhere.

Can users please test the latest explorer code on OS X in particular and
confirm that the toolbox is working for them? (I've done some testing on
both Windows and Ubuntu in fixing this.) You should see the same tools
listed in the Toolbox as are present on the Tools menu. The Tools > Add
Tool dialog ought to add tools into there instantly as well.

I'd also like some input from OS X users on
https://bugs.launchpad.net/bzr-explorer/+bug/518255. I'd like to fix
that before 1.0.0 as well, time permitting and assuming it's low risk.

Thanks,
Ian C.