The last change in ext/standard/string.c brought very bad inconsistency into 
dirname behaviour:

echo dirname("/foo/bar/")."/foobar";     =>    /foo/foobar
echo dirname("/foo/")."/foobar";         =>    //foobar

the function should everytime return a path with or without a slash at the end, 
but always the same.

I created a very simple patch that will stop returning a slash at the end in any
case:

--- string.c.orig       Sat Nov 18 17:00:28 2000
+++ string.c    Sat Nov 18 17:04:53 2000
@@ -714,8 +714,7 @@
        }
        if (end < path) {
                /* The path only contained slashes */
-               path[0] = DEFAULT_SLASH;
-               path[1] = '\0';
+               path[0] = '\0';
                return;
        }
 
@@ -735,8 +734,7 @@
                end--;
        }
        if (end < path) {
-               path[0] = DEFAULT_SLASH;
-               path[1] = '\0';
+               path[0] = '\0';
                return;
        }
        *(end+1) = '\0';