More copyright years updates.

Amends a001bb36fc1798e254fe1c218a79418bc0229dd5 with copyright lines I
forgot to update thanks to poorly chosen grep command.
VS: only include configurations of own projects in the solution.

Previously, .sln files contained all configurations from all included
projects (including Additional Dependencies pulled in from other
submodules) as solution configurations.  This led to having too many
configurations when e.g.  a third party dependencies contained
configurations that were only needed by a single submodule.

Instead, only include configurations from "own" projects, i.e.  those
defined in the corresponding bakefile module or its submodules.  Configs
of dependencies pulled in from elsewhere are now ignored.
Better check for "extension" property being set.

Don't just check if the property is explicitly set; instead, see if it
is unset or null.  Unlike the previous code, this works correctly when
the extension is overwritten conditionally, e.g.  only for some
toolsets.