bin/19635: add -c for grand total to df(1), like du(1) does

[Cyrille Lefevre]

anyone to commit this PR ? thanks in advance.

I'm using this patch for 2 years right now w/o any problems.

sample output :

# df -ch / /disk?
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/da0s1a    1.8G    1.6G     48M    97%  /
/dev/da1s1d    4.2G    3.8G     40M    99%  /disk1
/dev/da2s1d    4.2G    3.8G     39M    99%  /disk2
/dev/da1s1e    4.2G    3.7G    134M    97%  /disk3
/dev/da2s1e    4.2G    3.8G     60M    98%  /disk4
total           18G     17G    321M    98%

Cyrille Lefevre.
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home: mailto:cyrille.lefevre at laposte.net