install: validate gzip integrity before extracting
install: validate gzip integrity before extracting

This avoids cryptic errors from tarball extraction:

  gzip: stdin: unexpected end of file
  tar: Child returned status 1
  tar: Error is not recoverable: exiting now

By pointing out the cause of the error to the user:

  gzip: Apple_Guides_and_Sample_Code.tgz: unexpected end of file

sunaku/dasht