Determine a way to get the system default tmp dir when not set

[ZerooCool]

Dans la Todo list du développeur de la version 0.2.1 :

PhpSecInfo_Test_Core_Upload_Tmp_Dir::_execTest()
check for world-readable/writable perms on the existing dir ( A l'air OK ! )

**determine a way to get the system default tmp dir when not set ( Ne semble pas OK ! )**

Originally posted by @ZerooCool in #6 (comment)