Add tests for problems uncovered during forth self-hosted tests

tests/step4_if_fn_do.mal

@@ -43,6 +43,8 @@
 ;=>7
 (if (list 1 2 3) 7 8)
 ;=>7
+(= (list) nil)
+;=>false
 
 
 ;; Testing 1-way if form

tests/step9_try.mal

@@ -21,6 +21,10 @@
 ; "exc:" "my exception"
 ;=>7
 
+;;; Test that throw is a function:
+(try* (map throw [7]) (catch* exc exc))
+;=>7
+
 
 ;;
 ;; Testing builtin functions