Fixing regression.
CMake tweaks for Bro plugin.
Fix for Bro plugin.

Needed after recent change to plugins in Bro master.
Fix for some sink operations not flagging requiring safe points.

Also baseline updates.
Removing debugging relict.
Fixing another regression in Bro plugin.

Using both script compiler and pac2 analyzer was broken.
Refactor access to unit fields in BinPAC.

This funnels all accesses through a set of well-defined functions.
Union extensions and fixes, plus a struct extension.

We have union constructors now:

    type A = union {
        int<64> i,
        bool b,
        string test
    }

    type B = union<bool, string>

void run() {
    local A a
    local B b

    a = union<A>(test: "abc")
    b = union<B>("abc")
}

This actually works, too:

    a = union(test: "abc")
    b = union("abc")

The 2nd form create a union constant with just one field and then
coerces that on assignment.

Unions now also coerce to bool: true iff a value is set.

The commit also includes a few union fixes, plus a struct change:
fields can now be marked as "anonymous", meaning that when printed an
runtime their field name won't be shown. This can currently be set
internally on the AST node only, it's not exposed by the HILTI language.
Switching implementation of switch() statements to use unions
internally.

This comes with a slight change in output how "self" is printed in the
presence of a switch construct.
Fixing regressions.

Also a slight change in union output format: if the union has just a
single possible field, we don't bracket it in "<..>" anymore when
printing.