build - Add build-all and install-all targets

build - Add build-all and install-all targets

* Add a 'smart' build-all and install-all target that spews to a
  log file instead of to the screen and.   Will automatically
  run the build stage -j N, and both targets can be specified on
  one command line.

  make build-all install-all

  build-all:	runs buildworld and buildkernel -j hw.ncpu
  install-all:	runs installkernel and installworld -j 1

* The usual warnings and cautions still apply when installing a
  new world and kernel.