cmdutils: wrap exit explicitly

Some C runtime implementations deadlock when calling threading functions
on the atexit() handler.

Use a simpler wrapper similar to av_log to call the cleanup function
before exit.

Bug-Id: 523

cmdutils.h

@@ -44,6 +44,16 @@ extern AVFormatContext *avformat_opts;
 extern struct SwsContext *sws_opts;
 extern AVDictionary *format_opts, *codec_opts, *resample_opts;
 
+/**
+ * Register a program-specific cleanup routine.
+ */
+void register_exit(void (*cb)(int ret));
+
+/**
+ * Wraps exit with a program-specific cleanup routine.
+ */
+void exit_program(int ret);
+
 /**
  * Initialize the cmdutils option system, in particular
  * allocate the *_opts contexts.