- respect BLOCKSIZE env. var.(?)
- read blocksize from config(?)
- support df's -t arg for Linux
- do not show pseudofs unless -a given or config option is set (simulate Linux
  df behaviour at this point) (UPDATE: done for BSD)
- on Linux: for pseudofs do not show capacity and gauge 
- do we need to have system wide config like /etc/cdf.conf or ~/.cdfrc are quite enought?
- support df's -c
- add manpage