Show debug log messages on the console in the test when enabled

Using LogEnabler in wxFileSystemWatcher test case still didn't show
anything even in case of unexpected failures because debug messages
didn't appear in the test output.

Fix this by using a custom log target which shows the debug (and trace)
messages on stderr, instead of using the debug output for them, even
under MSW.

Also make LogEnabler public, and rename it to a more unique name, as it
could be useful in the other tests too.

tests/fswatcher/fswatchertest.cpp

@@ -34,27 +34,6 @@
 // local functions
 // ----------------------------------------------------------------------------
 
-#if wxUSE_LOG
-// Logging is disabled by default when running the tests, but sometimes it can
-// be helpful to see the errors in case of unexpected failure, so this class
-// re-enables logs in its scope.
-//
-// It's a counterpart to wxLogNull.
-class LogEnabler
-{
-public:
-    LogEnabler() : m_wasEnabled(wxLog::EnableLogging(true)) { }
-    ~LogEnabler() { wxLog::EnableLogging(m_wasEnabled); }
-
-private:
-    const bool m_wasEnabled;
-
-    wxDECLARE_NO_COPY_CLASS(LogEnabler);
-};
-#else // !wxUSE_LOG
-class LogEnabler { };
-#endif // wxUSE_LOG/!wxUSE_LOG
-
 // class generating file system events
 class EventGenerator
 {
@@ -161,7 +140,7 @@ public:
         ms_watchDir.AppendDir("fswatcher_test");
         REQUIRE(!ms_watchDir.DirExists());
 
-        LogEnabler enableLogs;
+        TestLogEnabler enableLogs;
         REQUIRE(ms_watchDir.Mkdir());
 
         REQUIRE(ms_watchDir.DirExists());
@@ -176,7 +155,7 @@ public:
         // just to be really sure we know what we remove
         REQUIRE( ms_watchDir.GetDirs().Last() == "fswatcher_test" );
 
-        LogEnabler enableLogs;
+        TestLogEnabler enableLogs;
         CHECK( ms_watchDir.Rmdir(wxPATH_RMDIR_RECURSIVE) );
 
         ms_watchDir = wxFileName();