Fix a few VM issues which were causing subtle failures in the test cases.

Includes a new VM method, newCall, which must be called before pushing
a call onto the stack to make sure that base is set correctly.
A couple of weird issues remain with autoload.lua.

src/test/res/calls.lua

@@ -0,0 +1,24 @@
+local function f(x)
+	-- tailcall to a builtin
+	return math.sin(x)
+end
+
+local function factorial(i)
+	local function helper(sum, n)
+		if n <= 0 then
+			return sum
+		else
+			-- tail call to a nested Lua function
+			return helper(n + sum, n - 1)
+		end
+	end
+	return helper(0, i)
+end
+
+local result1 = factorial(5)
+print(result1)
+print(factorial(5))
+
+local result2 = f(math.pi)
+print(result2)
+print(f(math.pi))