Clean up all the cruft after a pg_rewind test run.

regress_log temp directory was properly .gitignore'd, which may explain
why it got left out of the "make clean" action.

src/bin/pg_rewind/Makefile

@@ -45,7 +45,7 @@ uninstall:
 
 clean distclean maintainer-clean:
 	rm -f pg_rewind$(X) $(OBJS) xlogreader.c
-	rm -rf tmp_check
+	rm -rf tmp_check regress_log
 
 check: all
 	$(prove_check) :: local