proto: Fix for rare FileIn hangs. (RHBZ#969845).

Yet another protocol bug!

If the daemon cancels, then the library should send a cancellation
chunk.  It normally does this during the loop where it is uploading a
file.  However due to an oversight or possibly a regression when we
modularized the socket code, the library did not send a cancellation
chunk if the daemon cancelled just before the end of file was sent.

This commit fixes this.

src/proto.c

@@ -376,7 +376,14 @@ guestfs___send_file (guestfs_h *g, const char *filename)
     return -1;
   }
 
-  return send_file_complete (g);
+  err = send_file_complete (g);
+  if (err < 0) {
+    if (err == -2)              /* daemon sent cancellation */
+      send_file_cancellation (g);
+    return err;
+  }
+
+  return 0;
 }
 
 /* Send a chunk of file data. */