Comment 3 for bug 495131

The root of this problem is the inability of python's os.statvfs to handle ramfs file systems. A workaround
is to use tmpfs instead, then everything works. ...DistUpgradeCache.py has the checkFreeSpace function which utilizes the os.statvfs. The purpose of using a ram disk here is to minimize writes to flash, which has a limited number of write cycles. From the docs, it looked like ramfs would be better for this than tmpfs (I have no swap either), but since I can successfully run update-manager with the tmpfs, this fix should be low priority.