vagrant: use 32-bit default image

There are known bugs in the Frenetic stack related to 64-bit word size.
Until those are resolved, use 32 images as the default.
vagrant: lower memory limit

Err on the side of caution and allocate a small amount of memory to the
VM so that new users don't start unexpectedly thrashing.
vagrant: remove repeated 'wget'
vagrant: Use i386 packages for bison
Merge pull request #271 from frenetic-lang/vagrant

Updates to Vagrantfile