prevent multiple block editors on the same block definition, allow
multiple dialogs on different objects, handle dialog instances in
DialogBoxMorph.prototype
for new "scripts pic..." feature on the scripting area's context menu.
Also pushed up version dates for new beta release, and added
SnapManual.pdf to the help folder
Shift-clicking on the settings menu lets you specify a fraction, by
which blocks and scripts are scaled, allowing you to e.g. export
poster-sized hi-res script pics, or to present Snap! live on hi-res
screens and projectors