NetSurf #673 seems to have an aversion to all local html files, A "Warning
from Netsurf" box opens which just reports "Unknown". This occurs on the
ARMini and OS4.39 on VRPC. #672 is OK!
All I could find in the log is :-
(1.760000) riscos/gui.c warn_user 2308: Unknown (null)
The complete log is at http://pittdj.co.uk/temp/unknown.zip
minimalist html file sufficient to show the problem.