Soft Margins Cut Bombardier Profit  MONTREAL (Reuters) - Second-quarter profit fell by  two-thirds at plane and train maker Bombardier Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=BBDb.TO target=/stocks/quickinfo/fullquote"&gt;BBDb.TO&lt;/A&gt;  as its regional aircraft business lagged a rebound in the  business jet market, the company said on Wednesday.