Move Travis onto llvm-3.3

This updates Travis to use LLVM 3.3 instead of 3.2, and simultaneously heralds the arrival of 3.3 binaries on the PPA.  3.2 binaries are maintained alongside, so users can switch at their leisure, for now.

@JeffBezanson; do you want to move to 3.3 for the 0.2 release?  I can't find a reason not to, we have a PPA, Homebrew has a formula, and even Arch Linux has a package for it, so I don't think we're going to lack in distribution support.  If so, we can merge this, I'll change my nightlies to require 3.3 instead of 3.2, and we can change the requisite setting in `deps/Version.make`.  We just have to be careful to clear out anything having to do with LLVM in `usr/` after the version is changed in `deps/Version.make`.