Crude hack to solve

Crude hack to solve
  rmdir .../var/tmp/binpkgs/cat/pkg-ver: Invalid argument
and alike for var/tmp/portage/... on Solaris.

rmtree(2) returns EINVAL on Solaris if the argument (the dir to remove)
is the current directory, or the argument ends with '.'.  Since we cd to
PORTAGE_BUILDDIR we indeed cannot remove it anymore on Solaris.  Hence,
we now try to go to the parent of this dir, but ultimately a better
solution should be found.

svn path=/main/branches/prefix/; revision=11577