ZF-7281: Refactor Zend_Cache_Backend::getTmpDir()'s way to detect the temp dir

Description

Currently the function uses a loop to detect where the temp dir is. Since we now require PHP >= 5.2.4 we can use sys_get_temp_dir() instead

Comments

I was said that sys_get_temp_dir is not always available or returns proper data.

Also note that this methodology is available multiple times in the framework. Changing one means of course to change also the others.

If it's not broken don't fix it ;). Seriously though, while the change would be attractive there remains doubt about it's cross-system behaviour. For Zend Framework 2.0 the approach would be better suited if a unified approach was defined somewhere all components could utilise. Zend_Environment might be a possible target for this.