record some information about a bug
special-case handling for line-coalescing false positives
dramatically improve speed and memory usage

when looking for boring brackets, we used to unlines and re-lines the
entire file; now guess that the ending bracket will probably be in the
next few lines, hence keeping the lines-d version of the remainder of
the file

before:
parsing slow.log ~40 seconds
cabal test ~4 minutes, memory usage spiking around 1.5Gb

after:
parsing slow.log ~0.4 seconds
cabal test ~24 seconds, memory usage relatively flat and peaking at 80Mb
another slight performance tweak

instead of walking a list of regexen, compare to a single regex that
matches all the same stuff; results in ~20% speed boost across the board