SharedSolver was archiving too many constraints, partly because of
multiple typos, also because it archived some which were just artifacts
of the layout process. These extra constraints are created when the
layout calls SetRange() on the left/top/right/bottom tabs during layout.
* LinearSpec/ActiveSetSolver had to be adjusted to get access to the
constraints added by the SetRange() calls.
* BALM::TabBase was adjusted to avoid a segfault during unarchiving,
caused by an unitialized member.
* ALMFriendLayoutTest was adjusted to include a more obvious custom
constraint for testing.
c8b24e3eb5