(PUP-2711) Make recursive manifest parsing conditional to future parser

This makes the ability to load all .pp files under a manifest dir
recursively conditional to parser == future. (It will become the
standard in Puppet 4.0). This is done to avoid slurping in lots of files
in case users kept other files around in a subdirectory in the belief
that they would not be loaded. Thus making it harder to upgrade.

This also adds a test that runs for future parser.