[m-dev.] for review: fix lambda expr & debugging type_info bug

[Simon Taylor]

> compiler/polymorphism.m:
> 	When processing lambda expressions,
> 	add type_info variables for the argument
> 	variables, not just for the non-local variables.
> 	This is necessary for debugging in the case of 
> 	lambda expressions with unused arguments.

That looks fine, thanks Fergus.

Simon.