Wrapped binaries should emit information to a file rather than stderr

[JasonGross]

This might let us debug coq-tools. We'll have to be careful about parallel builds, maybe we should do something like exec >>(tee -a /path/to/log-file-`date +%s`-$$.stdout.log) 2>>(tee -a /path/to/log-file-`date +%s`-$$.stderr.log >&2) and that way we can get time-ordering and also a lack of parallel collision?