fix #527: some commands don't wind up in command history
fix #527: some commands don't wind up in command history

Looks like a recursive call to `Line.runInputT settings` interferes with the recording of history.
Moreover, only a `pure` value seems to flush things out to the `.unisonHistory` file.

unisonweb/platform,unisonweb/platform,unisonweb/platform