Speed up checklog again, and sundry fixes

Follow up to !71955 (merged) and fix for ATR-29535.

Apparently the regexes for lines to be ignored are much slower (more wildcards) than the backtrace and FPE regexes, so restored the previous order of the checks to maintain speed (I had tried to consolidate the logic).

Fixed another problem which was that the __builtins__ could omit all python error messages when the module is run, resulting in an empty regex matching the entire file as 'python errors'.

The change from re.search(pattern,line) to pattern.search(line) was in the process of trying to speed things up. No measurable effect, but I think it is still the syntax we want. Other changes are basically minor, defining get_parser() was mainly so I could profile.