contrib: check in a whitelist of passing tests in Python 3

tests: try and fail more gracefully with broken unicode escapes

md5sum: adapt for python 3 support

profiling: allow configuring minimum display threshold for hotpath statprof.display_hotpath() accepts a "limit" function to choose the minimum threshold for samples to display. The default is 0.05, which means you don't need individual items contributing less than 5%. I had a need to adjust this threshold. We already have a config option for it. So let's reuse it. check-config.py doesn't like having multiple defaults for the ui.configwith() calls. The behavior is obviously correct. I'm not sure if it is worth teaching check-config.py how to ignore this. So I've just accepted the new output.

config: document profiling.show{min,max}

check-config: look for ui.configwith We previously weren't looking for this config helper. And, surprise, profiling.py references config options without docs. If I tried hard enough, I could have combined the regexps using a positive lookbehind assertion or something. But I didn't want to make my brain explode. At some point, we should probably do this linting at the tokenizer or ast layer. I'm not willing to open that can of worms right now.

check-config: use named groups in regexp In preparation for making this regexp a bit more complicated.

check-config: use compiled regexp And split the regexp across multiple lines to make it easier to read.