Description:
------------
Stream wrappers which ultimately result in file operations which should be 
permitted by safe mode do not work in some circumstances. For example, a stream 
wrapper which simply stores files in sys_get_temp_dir() works fine without safe 
mode, but fails when that is enabled:

// copy 1: file to stream wrapper
$ok = copy('/tmp/source.txt', 'temp://destination.txt');

// copy 2: stream wrapper to file
$ok = copy('temp://destination.txt', '/tmp/source.txt');

// copy 3: SAME file as stream wrapper to file
$ok = copy(sys_get_temp_dir() . '/destination.txt', '/tmp/source.txt');

Under safe mode, the second copy fails with error message

   Warning: copy() [function.copy]: Unable to access temp://destination.txt in 
.../test-copy.php on line ...

This may be related to https://bugs.php.net/bug.php?id=46888


Test script:
---------------
http://drupal.org/files/test-copy.txt

Expected result:
----------------
All three file copies should succeed, since sys_get_temp_dir() returns a directory 
accessible to safe-mode.

Actual result:
--------------
Second copy fails. Third copy, which refers to the same files, succeeds.