Make some adjustments so that it's possible to install binary

Make some adjustments so that it's possible to install binary
packages without having a portage tree:

* Make portdbapi.aux_get() return early by raising a KeyError
  if it detects that there is no portage tree.

* Move the ARCH and USERLAND sanity check to the last moment
  in doebuild() and only require these variables if an
  existing environment (such as environment.bz2) is
  unavailable.

* Make the NewsManager constructor cope with a broken
  make.profile symlink.

svn path=/main/trunk/; revision=8973