Description:
------------
If you check a relative pathname with is_dir(), the result is cached.  However, chdir() does not invalidate that cache.  Thus, after a chdir(), is_dir() using the same relative pathname gives invalid results.

NOTE: In truth, I'm running PHP 5.2.5, not 5.2.6.  But this is on a professional hosting service, and I can't control the version.

Reproduce code:
---------------
<?
   // note that if you run this script multiple times, then all the
   // mkdir()s will give errors, since they already exist.  That's
   // irrelevant to the bug.

   // I put this all inside a subdirectory so as to not clutter up the
   // pwd of the script.  Again, irrelevant to the bug.
   mkdir("x");
   chdir("x");
      clearstatcache();

   // key reproduce code starts here
   mkdir("y");
   mkdir("z");

   var_dump(is_dir("z"));

   chdir("y");
   var_dump(is_dir("z"));    // this is where the bug is exposed
   var_dump(is_dir(getcwd()."/z"));

   clearstatcache();
   var_dump(is_dir("z"));
?>

Expected result:
----------------
bool(true)
bool(false)
bool(false)
bool(false)

Actual result:
--------------
bool(true)
bool(true)
bool(false)
bool(false)