Write stack traces to stderr (#481)

This will show up in the msbuild output with a higher importance by
default, and may also align more closely with the expectations of
command line users.

@marek-safar the other option is to make this the behavior of monolinker as well. What do you think?

src/linker/Linker/Driver.cs

@@ -61,9 +61,8 @@ public static int Execute (string[] args, ILogger customLogger = null)
 				driver.Run (customLogger);
 
 			} catch (Exception e) {
-				Console.WriteLine ("Fatal error in {0}", _linker);
-				Console.WriteLine (e);
-				return 1;
+				Console.Error.WriteLine ("Fatal error in {0}", _linker);
+				throw;
 			}
 
 			return 0;