Description:
------------
is_readable() and file_exists(), when called from a PHP 4.3.2 (Linux), 4.4.0 (Mac OS) and 5.2.1 (Mac OS) script that is executed with posix_euid() != posix_uid() does not recognize files that are owned and readable only by the effective uid.  Instead is_readable() and file_exists() return "false" even though functions like fileperms, fopen and readfile work as expected.

Reproduce code:
---------------
#!/usr/bin/php
<?php
echo "My effective UID is ".posix_geteuid()." but my UID is really ".posix_getuid()."\n";

chdir($curdir = dirname(__FILE__)) or die("Unable to enter the private directory");
echo "The current directory is owned by ".fileowner($curdir)." and has permissions ".sprintf('%o', fileperms($curdir))."\n";

touch("test.dat");
chmod("test.dat", 0600); // readable only by the effective user

echo "is_readable should give TRUE, and gives ".(is_readable("test.dat") ? "TRUE" : "FALSE")."\n";

echo "file_exists should give TRUE, and gives ".(file_exists("test.dat") ? "TRUE" : "FALSE")."\n";

echo "The file has permissions ".sprintf('%o', fileperms("test.dat")).", is owned by ".fileowner("test.dat")." and is in the ".filegroup("test.dat")." group.\n";

unlink("test.dat"); // no error because the file really does exist!

?>

Expected result:
----------------
My effective UID is 501 but my UID is really [uid]
The current directory is owned by 501 and has permissions 40700
is_readable should give TRUE, and gives TRUE
file_exists should give TRUE, and gives TRUE
The file has permissions 100600, is owned by 501 and is in the 501 group.

Actual result:
--------------
When run as its owner, gives the expected result, with [uid]=501.

When run from a different account using the executable obtained from
#include <unistd.h>

int main(int argc, char **argv) {
  execl("/path/to/reproduce_code.php", "/path/to/reproduce_code.php", NULL);

}
which is then chmod 04711 or 06711, gives

My effective UID is 501 but my UID is really 503
The current directory is owned by 501 and has permissions 40700
is_readable should give TRUE, and gives FALSE
file_exists should give TRUE, and gives FALSE
The file has permissions 100600, is owned by 501 and is in the 501 group.

These tests are done on Mac OS X 10.4.8 with both PHP 4.4.4 and 5.2.1, but I first noticed this behaviour with PHP 4.3.2 under Red Hat Linux for which I do not have root privileges.