Adds assert() for Nasal and fixes io.include internal marking

- A simple assert() function is added to the globals namespace.

 - io.include() marks the target namespace to avoid dependency loops.
   If the namespace is marked before the script to be included is
   compiled, a parse error leaves the target namespace marked while
   the script has not been loaded. This patch fixes this problem.

Nasal/globals.nas

@@ -27,6 +27,15 @@ var L2GAL = 1 / GAL2L;
 # container for local variables, so as not to clutter the global namespace
 var __ = {};
 
+##
+# Aborts execution if <condition> evaluates to false.
+# Prints an optional message if present, or just "assertion failed!"
+#
+var assert = func (condition, message=nil) {
+	message != nil or (message = "assertion failed!");
+	condition or die(message);
+}
+
 ##
 # Returns true if the first object is an instance of the second
 # (class) object.  Example: isa(someObject, props.Node)
@@ -180,4 +189,3 @@ settimer(func {
         if(size(file) > 4 and substr(file, -4) == ".nas")
             io.load_nasal(path ~ "/" ~ file, substr(file, 0, size(file) - 4));
 }, 0);
-

Nasal/io.nas

@@ -47,8 +47,6 @@ var include = func(file) {
     if (contains(ns, module))
         return;
 
-    ns[module] = "included";
-
     var code = call(compile, [readfile(path), path], var err = []);
     if (size(err)) {
         if (find("Parse error:", err[0]) < 0)
@@ -57,6 +55,7 @@ var include = func(file) {
             die(sprintf("%s\n  in included file: %s", err[0], path));
     }
 
+    ns[module] = "included";
     call(bind(code, ns, fn), [], nil, ns);
 }
 
@@ -425,4 +424,3 @@ _setlistener("/sim/signals/nasal-dir-initialized", func {
         }
     })();
 });
-