When overriding the python3 dependency of vapoursynth, it should get
propagated to all plugins. Currently, however, this causes
incompatibilities, because `vapoursynth.python3.callPackage` only sets
the `python` attribute, not `python3`. This currently causes build
failures due to different site-packages paths.
vapoursynthPlugins.addgrain: init at r7
vapoursynthPlugins.autocrop: init at 0.1
vapoursynthPlugins.beziercurve: init at r2
vapoursynthPlugins.bifrost: init at 2.2
vapoursynthPlugins.bilateral: init at r3
vapoursynthPlugins.bm3d: init at r8
vapoursynthPlugins.continuityfixer: init at 6.1
vapoursynthPlugins.descale: init at r2
vapoursynthPlugins.eedi2: init at r7.1
vapoursynthPlugins.eedi3m: init at r4
vapoursynthPlugins.f3kdb: init at 2.0.0-1
vapoursynthPlugins.ffms2: init as alias
vapoursynthPlugins.fmtconv: init at r20
vapoursynthPlugins.knlmeanscl: init at 1.1.1
vapoursynthPlugins.lsmashsource: init at unstable-2017-08-12
vapoursynthPlugins.nnedi3: init at 11
vapoursynthPlugins.retinex: init at r4
vapoursynthPlugins.sangnom: init at r41
vapoursynthPlugins.tcanny: init at r12
vapoursynthPlugins.tnlmeans: init at unstable-2015-02-25
vapoursynthPlugins.wwxd: init at 1.0