strip: also backup obsmarkers We are about to give 'strip' the ability to remove obsmarkers. Before we start removing data we must make sure it is preserved somewhere. So the backup bundle created by 'strip' now contains obsmarkers.

tests: fix run-tests when there's a bad #if in a test That has (and still does) caused the test to be skipped, but without this fix it was possible to exit this block of code without clearing the output channel, which poisoned the channel list for later test method runs. Fix this by always clearing the channel in a finally. The test for this is somewhat unfortunate. Sadly, I couldn't get a way to reproduce this with less than 2n+1 test cases, nor could I get it to reproduce reliably without the sleep statements. It's also crucial that the test with the broken #if be smaller (in terms of byte count) than the sleeping tests, so that it runs first and would poison the channel list prior to another test needing that entry from the list.

tests: make run-tests fail early if no channel is found I hit a weird corner case in run-tests where a test that caused an exception to be raised was breaking everything with an unbound variable error a few lines down because channel was never getting set in this for loop. By adding an `else` clause to this for loop, we can explode right away if we can't find a channel and give the developer a better chance at figuring out what's going on.

dispatch: convert exception payload to bytes more carefully We were previously depending on str() doing something reasonable here, and we can't depend on the objects in question supporting __bytes__, so we work around the lack of direct bytes formatting.

help: convert flag default to bytes portably We were relying on %s using repr on (for example) integer values. Work around that for Python 3 while preserving all the prior magic.

cmdutil: use isstdiofilename() where appropriate