Use $PVR instead of $PV for subslots

[hololeap]

Switch the default of

SLOT="0/${PV}"

to

SLOT="0/${PVR}"

e.g. ebuild revision bumps would trigger the rebuild of their immediate revdeps automatically

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If you modify the code for a package with a patch between version bumps, the revdeps will still need to be rebuilt. But, with the current setup, portage will not know this even if you make a revision bump for the ebuild. Using $PVR as the subslot instead of $PV would tell portage that the first level of revdeps need to be rebuilt, which could reduce some need to run haskell-updater between emerge failures.

The only downside I could see to this is if, for some reason, you needed to do a revision bump for the ebuild but did not touch the .cabal file, RDEPEND, or the code in any significant way. In this scenario, it would trigger a pointless rebuild of the first level of revdeps. However, this seems like it would be such an uncommon scenario that it wouldn't outweigh the usefulness of switching subslots to $PVR.

It would also mean people would need to be more thoughtful about why they are doing a revision bump for an ebuild.

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Thoughts?