[m-dev.] diff: module_qual.m import warnings

[Simon TAYLOR]

> compiler/module_qual.m:
> 	Don't warn about unnecessary interface imports of `string', `int',
> 	or `float', because such warnings are spurious in the common case
> 	where the interface uses the type string, int, or float.
> 	Also, make a few minor improvements to the error messages.
> 

> +		% We don't warn about modules `int', `float', or `string',
> +		% because those warnings are sometimes spurious.
> +		% (The types `int', `float', and `string' are defined
> +		% in mercury_builtin.m, but arguably they ought to be
> +		% defined in int.m, float.m, and string.m, and so if someone
> +		% uses the type `int' in the interface, then we don't warn
> +		% to warn about `import_module int' in the interface.)

This comment is a little misleading in that int, float and string aren't
actually defined in any module. Throughout the compiler, int is referred 
to as unqualified("int") not qualified("mercury_builtin", "int").

Other than that, those changes look fine.

Simon.