Merge pull request #451 from matthiaskrgr/PKGBUILD

Pkgbuild
ebuild: depend on <dev-lang/v8-3.16.5
ebuild: rebuild on v8 subslot change
scriptengine: don't use deprecated API

fixes #450
ebuild: we are now compatible with upstream v8 on master
Merge pull request #453 from karolherbst/bug450

we should not use v8::Externel::(Un)wrap anymore

fixes #450