Clean up after pg_dump test runs.

The tmp_check directory needs to be removed by "make clean",
and also ignored by .gitignore.

src/bin/pg_dump/.gitignore

 /pg_dump
 /pg_dumpall
 /pg_restore
+
+/tmp_check/

src/bin/pg_dump/Makefile

@@ -53,3 +53,4 @@ uninstall:
 
 clean distclean maintainer-clean:
 	rm -f pg_dump$(X) pg_restore$(X) pg_dumpall$(X) $(OBJS) pg_dump.o common.o pg_dump_sort.o pg_restore.o pg_dumpall.o
+	rm -rf tmp_check