set -e (was: parallel build failure with .c.o rule interrupted mid-step!)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

> -e you know I think (it was created, I have always believed, just 
> for make to use, so using it there makes sense, but that's about 
> the only time anyone should ever use it)
I find it quite useful outside of make (in cases I either forget adding 
|| errror "blah" in some places or it's too clumsy).