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-expected.out

@@ -0,0 +1,4 @@
+15
+15
+1.2246467991473532E-16
+1.2246467991473532E-16