Fix test_multi_tree crash on indexing.
Remove the directory_index config directive.

It is no longer necessary, since we're rendering folder listings at request time rather than laying them down on disk.
Remove the filter_language config directive.

Instead, we'll be showing the filters registered by the enabled plugins on each tree.
Increase Vagrant RAM to 1GB.

Since we started running ES, People have been terrorized by the kernel's out-of-memory killer while running make.