help: add missed last new line to "internals" topic Caught by test-gendoc.t.

dirstate: make delaywrite sleep until the next multiple of n seconds Rather than sleep for 2 seconds, we sleep until the next even-numbered second, which has the same effect, but makes tests faster. This removes test-largefiles-update as the long pole of the test suite.

dirstate: only invoke delaywrite if relevant This avoids a significant amount of sleeping in some of our longest tests.