[PATCH] Display decoded IDNs

Hi I finally got round to the second part of my IDNA work, which is allowing the decoded versions of the domain names to be displayed in the status and URL bars. This adds an option display_decoded_idn (default is false) which, when enabled, will pass decoded UTF-8 URLs to the status bar and - with an appropriate frontend tweak (I've done GTK, RISC OS and Amiga) - also to the URL bar. When switched off operation is as at present and the code change is minimal. This is in branch chris/display-idna and attached for convenience. Chris