nrelease - Release build adjustments

nrelease - Release build adjustments

* Add GITHOST override to Makefile.usr

* For now checkout 2010Q3 by default in master, this will be changed
  to 'master' in a month or two but for now we want to match the release.

* Add GITHOST feature to the nrelease Makefile, defaulting to
  git.dragonflybsd.org.  This allows developers who do release builds
  to specify a more local clone/mirror/copy of the pkgsrcv2.git and
  dragonfly.git repos.

  nrelease pulls from these repos so this can save a bunch of time.

* nrelease now installs each kernel into its own kernel.XXX directory
  in /boot, with a complete set of modules for each kernel.  This is
  instead of installing all kernels into /boot/kernel/ and naming them
  differently inside /boot/kernel/.

  This is to conform to the recent dloader work and very recent new
  menu features.

* All kernels+modules are installed with INSTALLSTRIPPEDMODULES so the
  ISO comes in at a reasonable size.

* The release ISO now contains both a UP and a SMP kernel, selectable
  at boot time.

* Do not try to include pkgsrc in the release ISO/IMG (at 1G+ it is too
  big).  We continue to include system sources.  There isn't enough room
  for full sources in the ISO/IMG.  Note that GUI builds will include
  a full pkgsrc and full sources, including a .git base for them.

* nrelease now supports a IMGSIZE override on the make line (in sectors),
  for the usb image.

* nrelease now autosizes the IMG file (when not overriden by IMGSIZE) to
  the nearest base-10 gigabyte to ensure that it fits on the USB stick
  and provide a bit of extra space for messing around.