Fix a typo. In this case, the typo caused the f_noyes() invocation to
display a global instead of the passed-argument; however since the global
always has the same value as the passed argument, it made no difference in
the realtime operation.
Like r250701, introduce another handy function for truncating variables to a
specific byte-length. Works like vsnprintf(3).
Move ppp.8.m4 back to ppp.8 and de-ifdef it.

Requested by: joel

MFC after:	1 week