macOS's stat does not support -c %s', use -f %z' instead

[clarkwang]

No description provided.

[clarkwang]

Better use full pathname (/usr/bin/stat) in case another stat is installed (e.g. by Homebrew)?

[jeffpc]

Two things:

1. This os-sepecific behavior should be put into os.* files.
2. Guilt is not maintained anymore: https://blahg.josefsipek.net/?p=598

[shadowbase7]

.

[fziglio]

Trying to collect a bit of changes and doing some fixes. See https://github.com/freddy77/guilt/. This specific issue is fixed by freddy77@91dfe4d using os.XXX files.