Support for Windows 7 jump lists (right-click on a program's taskbar

Support for Windows 7 jump lists (right-click on a program's taskbar
icon, even if the program isn't running at the time, to be presented
with an application-defined collection of helpful links). The current
jump list is updated every time a saved session is loaded, and shows
the last few launchable saved sessions (i.e. not those like Default
Settings) that were loaded. Also, if Pageant or PuTTYgen or both is in
the same directory as the PuTTY binary, the jump list will present
links to launch those too.

Based on a patch sent last year by Daniel B. Roy, though it's barely
recognisable any more...

git-svn-id: http://svn.tartarus.org/sgt/putty@9046 cda61777-01e9-0310-a592-d414129be87e