Fix package selection logic in order to prevent downgrade in cases
when selective is True and the currently installed version does
not have a matching ebuild in the tree. For example, this type of
situation is likely to occur if the user somehow obtains a binary
package that has a newer version than any of the ebuilds in the
portage tree. If package maintainers want to encourage a downgrade
in a case like this then they should use package.mask so that the
user receives a warning about the installed package being masked.
svn path=/main/trunk/; revision=9336