b: not exist
b/b.txt: not exist
-Makefile:14: *** a exists in /home/kazubito/2010_11/autotest.mk/selftest/unittest/chk_file_ext. 中止.
-Makefile:18: *** a/a.txt exists in /home/kazubito/2010_11/autotest.mk/selftest/unittest/chk_file_ext. 中止.
+Makefile:13: *** a exists in $PWD. Stop.
+Makefile:17: *** a/a.txt exists in $PWD. Stop.