check-diskfree ignores fs with "media" anywhere in mount path

check-diskfree attempts to exlucde external automatically mounted disks by removing mount paths containing "media/" from the output of df(1), like so:

    df -klP |
    grep ^/ |
    grep -v /media/ |
    ...

If you have a standard filesystem mounted at, say, /mnt/media/press (any mount point with media as the non-terminating component), then this will be unintentionally excluded.

Suggested fix:

    42c42
    < grep -v /media/ |
    ---
    > grep -v ^/media/ |