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/autoload.lua

@@ -1,11 +1,14 @@
+-- Clear out builtin math package
+math = nil
+
 local function autoload(table, key)
-	local chunk = loadfile("/"..key..".luac")
+	local chunk = loadfile(key..".luac")
 	table[key] = chunk()
 end
 
-autoload_mt = { __index = autoload }
-
-setmetatable(_G, autoload_mt)
+setmetatable(_G, { __index = autoload } )
 
+-- local result = math.sqrt(9.0)
+-- print("x=", result)
 print("square root of 9.0 is ", math.sqrt(9.0))
 print("math.pi=", math.pi);