Add a tidy check to find unexpected files in UI tests, and clean up the results
While looking at UI tests, I noticed several weird files that were not being tested, some from even pre-1.0. I added a tidy check that fails if any files not known to compiletest or not used in tests (via manual list) are present in the ui tests.
Unfortunately the root entry limit had to be raised by 1 to accommodate the stderr file for one of the tests.
r? `@fee1-dead`
