Update Inno Setup script. Tested with IS 5.0.8 on Win98SE; I think there are

Update Inno Setup script. Tested with IS 5.0.8 on Win98SE; I think there are
a few things that will faze whatever we're using currently (2.0.19 or
thereabouts?), but nothing desperately modern. (NB, the 0.57 putty.iss works
fine with 5.0.8 and the installer is even 40k smaller.)

Notable changes:
 - Uninstallation now runs a variant of `putty -cleanup'. The variance is
   only in the text displayed; the user is still prompted, and the default
   action is (now) "keep" in both cases.
 - Optionally add an icon in the Quick Launch bar.
 - Make desktop item optionally for all users. (not tested)
 - "Create a Start Menu group" now handled via IS' own mechanism.

[originally from svn r5423]