Merged from trunk 585{1,9}

Merged from trunk 585{1,9}

Don't use os.path.isdir() because it can swallow errors related to
filesystem/disk corruption.

add some new tests (WarnerBro)

rename file (WarnerBro)

Round one of dep_getusedeps() (WarnerBro)

increase test coverage to cover slots, uncovering a few corner cases
that need fixing (WarnerBro)

fix regression in test changes (WarnerBro)

Load the most current variables from /etc/profile.env for post_emerge
stuff.

Fix --newuse so that it works correctly with --usepkg.

svn path=/main/branches/prefix/; revision=5861