Function declarations don't create a block where the variables listed
    in the parameter list are declared.  Because there are no variables
    declared, the types of the parameter variables is unchecked, allowing
    for invalid values to be used as the type.  This patch adds a special
    case to the check_types pass for function declarations.
    
    Fixes golang/go#11567.
    
    Reviewed-on: https://go-review.googlesource.com/12662

From-SVN: r226456