test: failing 100-sed-autoconf-dirname test.

check.sh

@@ -144,6 +144,7 @@ tests='
 100-sed-undo
 100-sed-file
 100-sed-fooRbar
+100-sed-autoconf-dirname
 
 100-tar
 100-tar-Z

test/100-sed-autoconf-dirname.sh

@@ -0,0 +1,15 @@
+dirname='/^.*\/\([^/][^/]*\)\/*$/{
+	    s//\1/
+	    q
+	  }
+  /^X\/\(\/\/\)$/{
+	    s//\1/
+	    q
+  }
+  /^X\/\(\/\).*/{
+	    s//\1/
+	    q
+  }
+  s/.*/./; q'
+
+echo 'X/foo/bar' | \sed "$dirname"

test/100-sed-autoconf-dirname.stdout

@@ -0,0 +1 @@
+bar