Fixes #941

Most doubles that are delivered via respondd have limited input
precision, but are converted with up to 17 digits of precision. That can
cause ugly blowups like 0.2800000000000001 in the output, which is
avoided by specifying better format strings (like "%.2f" in most cases).

This include wasn't actually missing, but well hidden behind the iwinfo.h
include. Make this more obvious.

Should be redundant after 0bd0df6f

gluon-announced and gluon-announce are merged to gluon-respondd.