Make -o/-i arguments mutually exclusive
Right now, it's possible to specify both
-i at the same time, which doesn't make any sense.
Also, it's rather non-intuitive that both argument defaults are
True and that setting either of them changes their value to
I found this issue while working on legacy/trac#34216 (moved), but this issue seemed sufficiently different to justify having its own ticket. I'll post a patch for review in a minute.