Add framework to test error messages and argument type checking.

src/test/errors/baselibargs.lua

@@ -0,0 +1,9 @@
+package.path = "?.lua;src/test/errors/?.lua"
+require 'args'
+
+
+-- arg types for basic library functions
+local notastrnumnil={true,{},print}
+checkallpass('dofile', {{nil,'src/test/errors/args.lua','args.lua'}})
+checkallfail('dofile', {notastrnumnil})
+checkallerrors('dofile', {notastrnumnil}, 'bad argument')