Colorize javac errors

You know those multi-line ones that are frequently interspersed with other buld output?
The ones that don't even have the word "error" in them to search for?

This makes them red.

ps2: fix jar_check failures cause by leaving empty stderr files in intermediates dirs
     this is probably not the best place to store stderr before colorizing it if javac
     exits non-zero, but it seems much lighter than mkdiring a bunch of temp directories
     or using sed to mangle the paths to point to per-intermediates directory unique
     temporary file names