Alert user to drop-outs during recording...

1) When the program detects this, insert zeroes into the recording to keep the
other good parts synchronized.

2) When recording stops, a message box alerts the user, and a label track is
added showing the lost parts, labelled with consecutive numbers.

3) A menu item visible in alpha builds only is added to Tools, to simulate
recording errors at random times and test the reporting feature.

src/Menus.h

@@ -509,6 +509,7 @@ void OnBenchmark(const CommandContext &);
 #if defined(EXPERIMENTAL_CRASH_REPORT)
 void OnCrashReport(const CommandContext &);
 #endif
+void OnSimulateRecordingErrors(const CommandContext &);
 void OnScreenshot(const CommandContext &);
 void OnAudioDeviceInfo(const CommandContext &);
 #ifdef EXPERIMENTAL_MIDI_OUT