walkenfs improvements

I've made some progress towards my goal of making walkenfs usable by those who know nothing about Erlang or Mnesia.

• schemafinder has been open sourced, which provides Mnesia auto-configure.
• mount and umount work (although the mount line is very baroque), so no need to start an Erlang emulator explicitly.
  
• the distribution includes an example init script very close to the one we actually use.
  

Of course walkenfs could still have a showstopping bug in it. In our recent use it was mostly fuse mount options that gave us trouble, and also the shared writeable mmap problem surfaced because rrdtool uses that by default. fortunately with rrdtool, it was a simple configure option to disable mmap. We did have a data corruption scare in development but that turned out to be due to the default redundancy setting being 1 copy (changed that to 3, now that fragmentron can initialize under infeasible conditions). Otherwise, so far so good, knock on wood.