Refactor / idempotent-fy vagrant.sh

Big changes:
1) Update packages!
2) Remove uncessary X11 packages (wisely, before updating all the packages)
3) Install all packages at once
4) Leave package addition in same order, because, it looked interesting?
5) Look for symlink before making it (Vagrant errors out on second
   provision otherwise)
6) Build demboyz

vagrant.sh

@@ -4,10 +4,24 @@
 sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
 sudo apt-get update
 
-sudo apt-get install build-essential -y
+# Remove X11 cruft
+sudo apt-get autoremove -y
 
-sudo apt-get install gcc-4.9 g++-4.9 -y
-sudo apt-get install gcc-4.9-multilib g++-4.9-multilib -y
+# Keep things up to date
+sudo apt-get upgrade -y
 
-sudo apt-get install clang-3.6++ -y
-sudo ln -s /usr/bin/clang++-3.6 /usr/bin/clang++
+packages=""; # Start with nothing; can re-order rest to heart's content
+
+packages="$packages build-essential"
+packages="$packages gcc-4.9 g++-4.9"
+packages="$packages gcc-4.9-multilib g++-4.9-multilib"
+packages="$packages clang-3.6++"
+
+sudo apt-get install -y $packages
+
+# Why doesn't clang do this for us?
+[ ! -e /usr/bin/clang++ ] && sudo ln -s /usr/bin/clang++-3.6 /usr/bin/clang++
+
+# Build it!
+cd /vagrant/premake
+/bin/bash gmake.sh && { cd gmake; make; }