QStorageInfo: bytesAvailable(), bytesFree(), bytesTotal() are calculated incorrectly on Unix systems

struct statvfs contains a not exactly intuitive quirk: the f_blocks, f_bfree and f_bavail members refer to the number of fundamental blocks ("fragments"), whose size is given in f_frsize and not, as one might guess, in f_bsize. To make matters worse, f_bsize is often equal to f_frsize, except when it isn't (e.g. on a tmpfs).

Qt gets it wrong.