Kill the ffmpeg process in LoadFFmpeg's destructor.

This avoids a broken-pipe warning from ffmpeg when using -l.

(Strictly this will only work properly in CPython, since other
implementations like PyPy don't guarantee the destructor will actually
be run. Fixing this properly would mean changing the loader interface to
have an explicit close() operation.)

lddutils.py

@@ -336,6 +336,11 @@ def __init__(self, input_args=[], output_args=[]):
         self.rewind_size = 2 * 1024 * 1024
         self.rewind_buf = b''
 
+    def __del__(self):
+        if self.ffmpeg is not None:
+            self.ffmpeg.kill()
+            self.ffmpeg.wait()
+
     def _read_data(self, count):
         """Read data as bytes from ffmpeg, append it to the rewind buffer, and
         return it. May return less than count bytes if EOF is reached."""