The purchase of satellite imaging company DigitalGlobe by Canada’s MacDonald, Dettwiler & Associates Ltd. will likely end the DigitalGlobe’s history of buying satellites made by Colorado-based companies. The shift comes just as Westminster-based DigitalGlobe (NYSE: DGI) plans a $600 million system of satellites it hopes to start launching into orbit as soon as 2020. DigitalGlobe and Vancouver, Canada-based MDA announced reaching agreement on a $2.4 billion cash-and-stock merger transaction…