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- use_enable/use_with; make use_enable/use_with 3rd arg form match pms in eapi4,
match long standing portage behaviour for eapi's 0 through 3.
- when combining repository and slot restrictions in an atom, repository is now
always prefixed with ::, not intermixed. sys-apps/portage:0::gentoo for
example specifies slotting 0, repository gentoo.
- fixed a bug in installed pkgs virtual cache staleness detection- this
accounted for a surprisingly hefty ~25% for simple pquery invocations.
- fix typo in env protection code- load the scrubbed env, not the raw source.
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