test-bad-extension: reduce dependencies on other things test-bad-extension would jitter if the format of the first line of hg help changed, which isn't relevant to its goal.

help: fix help argument parsing and documentation support combining -c and -e previously -k was misdocumented: * the first line didn't mention it * the help half implied you could do help -k keyword topic with these changes, -k just changes the search method support -c and -e for -k searches