Don't do automagic reopening in VSC

Rename vf variables to fantom

Keep a list of fantoms for the points, and point the points to
these. This gets rid of the fantom struct on each point, and allows
for StillValid checking on groups at a time instead for each point.

Rename point's class to type to be consistent with VSM terminology

More class->type renames

Drop the type and ident pointers from VSC_point, and use the fantom's
pointers instead.

Reenable building of varnishstat

Don't assert on VSM file closed in VSC_Iter. It's safe to proceed
anyways and will produce a zero result in that case. This makes the
function consistent with how the other functions behave.