title: Programmatically find whether installing from unknown sources is allowed
body: <p>I need to find whether the current Android device allows to install apps from sources other than the market. This option appears in the settings UI under Applications named "Unknown sources".</p>
  
  <p>The setting basically allows you to download and install APKs that did not originate from the Google app market.</p>
  
  <p>How do I check whether this flag is on or off using code?</p>