Conversion cost ignores type parameters

[f37yu]

The conversionCost function incorrectly produces a cost of zero between parametric types.

with declaration

forall (dtype DT)
struct A;
A(int) aint;

the invalid cast

(A(char)) aint

is accepted by the compiler.

There is an algorithmic error in conversionCost: struct types are already handled in typesCompatible call, which correctly considers type parameters. However, incompatible structs are passed into ConversionCost? pass again which only consider names and not parameters.

[ajbeach]

Used the suggested fix (simply removing the offending code) and added a test that shows the error.

Commit: 1d179399a54c3ddcecf129adeec6303b1492ddac