Add a new reporter customization point: reporting all assertions

By opting the JUnit and XML reporters into it, we no longer run
into problem where they underreport the results without `-s` flag.

Related to #1264, #1267, #1310

include/reporters/catch_reporter_tap.hpp

@@ -30,9 +30,7 @@ namespace Catch {
         }
 
         ReporterPreferences getPreferences() const override {
-            ReporterPreferences prefs;
-            prefs.shouldRedirectStdOut = false;
-            return prefs;
+            return m_reporterPrefs;
         }
 
         void noMatchingTestCases( std::string const& spec ) override {