[mojosetup] Suffix for Mojosetup-Installers

[Ryan C. Gordon]

> It seems that the final Aquaria installer uses .mojo.run - does this mean, that we can agree on
> .mojo.run/.mojo?

I thought mojo.run was a good idea for self-extracting installers (and 
.mojo for ones that aren't self-extracting, if that ever becomes 
desirable), so I figured I'd try it out with Aquaria in the Humble Indie 
Bundle.

--ryan.