Hardens the src_install phase by validating that the expected image
exists in the downloaded package, and dies if copying those files to
"$ED" fails.
Signed-off-by: Itai Ferber <itai@itaiferber.net>
`swift-bin` is currently only built for amd64 and doesn't work on other
architectures; the KEYWORDS need to reflect this.
Signed-off-by: Itai Ferber <itai@itaiferber.net>