Converting a CmdlineArg straight to a Filename allows us to make the
filename out of the wide-character version of the string on Windows.
So now filenames specified on the command line should generally be
able to handle pathnames containing Unicode characters not in the
system code page.
This change also involves making some char pointers _into_ Filename
structs where they weren't previously: for example, the
'openssh_config_file' variable in Windows Pageant's WinMain().
Using a new screenshot-taking module I just added in windows/utils,
these new options allow me to start up one of the tools with
demonstration window contents and automatically save a .BMP screenshot
to disk. This will allow me to keep essentially the same set of demo
images and update them easily to keep pace with the current appearance
of the real tools as PuTTY - and Windows itself - both evolve.
