Unit test added/modified for fibers.

test/unittest/fiber.gravity

@@ -13,9 +13,9 @@ func main() {
     });
     
     g += 1;
-    fiber()
+    fiber.call()
     g += 1;
-    fiber()
+    fiber.call()
     g += 1;
     
     return g;

test/unittest/fibers_scheduling.gravity

@@ -15,7 +15,7 @@ func main() {
         for (var i in 1...n) {g += "c"; Fiber.yield();}
     });
     
-    for (var i in 1...n) {task1();task2();}
+    for (var i in 1...n) {task1.call(); task2.call();}
     
     g += "d";
     return g;

test/unittest/optimizer_fix.gravity

@@ -0,0 +1,9 @@
+#unittest {
+	name: "Check optimizer fix.";
+	result: 1320;
+};
+
+func main() {
+    var i = 13;
+    return 20 + i*100;
+}