Description:
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I'd like to propose making new php.ini var - open_basedir_include_dir - like 
safe_mode_include_dir , which would allow accessing one dir (files only in it) 
when open_basedir is set to other dir. Usual aplication of this would be "/tmp".

Since 5.3.x php allows tightening open_basedir. However tempnam() function 
(http://www.php.net/manual/pl/function.tempnam.php) does require as first 
parameter dir name. It does not take it from any php.ini var. So programmers had 
to hardcode in almost every program something like tempnam("/tmp",.... 
This makes open_basedir tightening useless as /tmp will remain unaccessible so 
tempnam() will fails. Solution would be open_basedir_include_dir ...