fix SEGFAULTs

issue was that mutable context had no config thus trying to get stream
caused SEGFAULT

Closes #1533, #1534

include/internal/catch_list.h

@@ -31,7 +31,7 @@ namespace Catch {
 
     std::size_t listReporters();
     
-    Option<std::size_t> list( Config const& config );
+    Option<std::size_t> list( std::shared_ptr<Config> const& config );
 
 } // end namespace Catch