The main runner now accepts -t for tags.

By default, the main runner will assume an untagged mode, because that's what
most tests are written for. Only mod_lily should be in tagged mode by default.

This allows people to simulate what tagged mode would do without actually
using mod_lily.
printfmt: Use d for integers, f for doubles.

It's Lily's fprintf, so it should act like it. To use special formatting flags
is probably going to confuse people. I know I've been confused by it myself
before.