Add more functions to the hh_single prelude

Summary: Tracking down a bug, wanted to have these available. Didn't add
newlines to avoid rerecording every test with a line number in the
prelude :\

Reviewed By: @int3

Differential Revision: D1728992
Autostart hh_server when doing `hh_client prolog`.

Summary: Basically just copypasta of the logic in hh build

Reviewed By: @jwatzman

Differential Revision: D1724674

Signature: t1:1724674:1418080627:f5785df6465f878398cd3d071632b98b508005f9