Merged from trunk 5060:5075

Merged from trunk 5060:5075

Pull in the new-style virtuals and install them so that the vdb has
complete standalone dep info, in case a portage tree isn't available.

For bug #141118, make dep_zapdeps assign zero cost to new-style
virtuals.

Revert the depclean message, since new-style virtuals will now be kept.

Update the _expand_new_virtuals docstring with a not about zero cost for
new-style virtuals.

Fix _expand_new_virtuals so that it doesn't allow any virtual deps to go
unaccounted for.

Integrate old-style virtuals handling into _expand_new_virtuals() and
prefer new-style over old-style whenever they are available.

For bug #155484, apply PORTAGE_NICENESS as soon as possible (especially
before global updates).

Make fixpackages use PORTAGE_NICENESS.

svn path=/main/branches/prefix/; revision=5077