Description:
------------
After writing to a compress://zlib stream, ftell() reports the
number of uncompressed bytes which have been written, not the
actual stream position.  This is inherently tied to the way the
streams layer works: the stream's write method is supposed to
return the number of input bytes processed, so the same confusing
behavior happens for all streams for which the number of input
bytes is not the same as the number of output bytes.

Since this cannot easily be fixed, it should at least be
documented.


Test script:
---------------
<?php
$s = fopen("compress.zlib://file.gz", "w");
var_dump(fwrite($s, str_repeat("hello world", 100)));
fflush($s); // this doesn't make a difference
var_dump(ftell($s));
fclose($s);
var_dump(filesize("file.gz"));
?>


Expected result:
----------------
int(1100)
int(38)
int(48)


Actual result:
--------------
int(1100)
int(1100)
int(48)