Upload.php - automaticly use sites/assets/cache for uploads

I had some issues with SAFE_MODE (being enabled) - tempnam() failed no matter what i tried and the upload_tmp_dir overwrite option didn't work.

**Upload.php** will now automatically use ***site/assets/cache/*** for temp-files, if everything else fails.

Maybe I'm missing something - but is there any particular reason for having to set ***$config->uploadTempDir*** manually when we already have write-access to the folders in ***site/assets*** ?


 ***site/assets/tmp*** would make more sense, but i wanted to use a path that PW has by default :)