Speed up build phase with "make -j"

[Anders F Björklund]

Weissmann Markus:

> Yes, but I meant this to be a per-Portfile choice so a maintainer can 
> mark his/her port as being able to build in parallel. Doing this with 
> the sledgehammer for all ports that use 'make' might be a bit too 
> much. ;)

It is supposed to be the default... But broken ports might need some 
way of signalling so, maybe "build.jobs 1".

> For build.nice it might be cool++ to do change the nice level for 
> port(1) directly so all phases run with low priority, not just the 
> build phase.

"nice port" ? I'm not sure if Mac OS X has ionice, but it might be 
useful for resource hogs like e.g. bzip2...

--anders