Add btests for new functionality

- Expand language.set to cover sets of sets
- Expand language.table to cover tables indexed with tables
- Add language.table-nested-set-ordering to capture the reproducer from GHI-1753

testing/btest/language/table-nested-set-ordering.zeek

@@ -0,0 +1,25 @@
+# This testcase used to cause subtle memory overflow problems due to deviating
+# traversal order of the k$a set members. With 4.2, this will trigger an
+# InternalError due to new bounds-checking. For context, see GHI-1753.
+#
+# @TEST-EXEC: zeek -b %INPUT >out
+# @TEST-EXEC: btest-diff out
+
+type Key: record {
+  a: set[string];
+  b: string &optional;
+  c: string &optional;
+};
+
+global state: table[Key] of count = {};
+
+event zeek_init() {
+
+  local k: Key;
+
+  k$a = set("MD5", "SHA1");
+  k$b = "12345678901234567890";
+
+  state[k] = 1;
+  print k;
+}