This fixes #916 , but I found another #1019 may duplicates this.
Check isatty existence on sys.stdout
And #1019 has a reference to #1022 as well. Fun times. Will figure out some combo that applies to recent bugfix branches (if this one doesn't, but it probably does) and credit errybody.
I also need to apply this to the corresponding code (just updated recently) in Invoke so Fab 2 doesn't regress.
Changelog re #1019, closes #1019, closes #1022, closes #1186