Always show vertical scroll bar

Some pages at tup website have small size and fit a screen. Some other
pages need several screens - it makes vertical scrolbar visible.

Tup website uses 'rubber' layout and position of menu depends on width of
screen. When we switch between pages with/without scroll the menu position
shifts, it looks ugly.

Always show scrollbar to make screen width and menu position stable
during page browsing.
Update copyright year at the website
Save both a full graph and trimmed graph when hitting a fatal circular dependency error.

The circular dependency may be discovered early in processing a large graph, so dumping the whole thing may not be useful in this case. We can trim the graph down to just the circular part by removing all nodes that either have no incoming links or no outgoing links, and then save the result. This should make the circular dependency more obvious to the user.
Make 'tup graph' behave similarly to the updater graph.

Perhaps this function should be made common somewhere...
Share graphing code among 'tup graph' and dump_graph().
Save graphs if we find a circular dependency during graph building.
Support 'tup varsed' on Windows.

This involves passing down the full path to the vardict file in the dll injection code, and making an mmap() compatible function using CreateFileMapping() / MapViewOfFile().
Update man page with correct options paths on Windows.
Merged recent changes.