Checks if an application is pristine (untampered) and from the official Mac App Store.
For technical details, see the blog post; "Are you from the Mac App Store?"
Code inspired by: RVNReceiptValidation
$ /fromAppStore /Applications/1Password.app
checking if 1Password.app is from the OS X App Store
app is signed with an Apple Dev. ID
found receipt at: /Applications/1Password.app/Contents/_MASReceipt/receipt
check 1 passed: bundle ID's match
check 2 passed: app versions match
check 3 passed: hashes match
verfied app's receipt; it's from the OS X App Store!