In C, %f and %F mean the same thing.

In Go, they are synonyms when scanning but %F is only accepted for complex numbers,
where it produces gibberish. It's easy and safe to make it work; it'a also easy and safe
to take it out for printing but leave it in for scanning. I favor making it work for
printing floats and complexes but could be talked into taking it out.

For scanning, though, it should stay.

Resolve for 1.3.