Fixes for

BUG#4506 "mysqlbinlog --position --read-from-remote-server has wrong "# at" lines",
BUG#4553 "Multi-table DROP TABLE replicates improperly for nonexistent table" with a test file.
It was not possible to add a test for BUG#4506 as in the test suite we must use --short-form
which does not display the "# at" lines.

client/mysqlbinlog.cc

@@ -723,8 +723,8 @@ static int dump_remote_log_entries(const char* logname)
     */
     if (old_off)
       old_off+= len-1;
-    else
-      old_off= BIN_LOG_HEADER_SIZE;
+    else                        // first event, so it's a fake Rotate event
+      old_off= position;
   }
   return 0;
 }