Confusing error messages when overload is missing but others are still there

[jrudolph]

As seen in akka/akka-http#3475.

In that case, an overload was replaced by a bunch of other ones. One of new ones matched the parameters but not the new return type which gave a IncompatibleResultTypeProblem. The others had different return type and parameter types which lead to another IncompatibleMethTypeProblem.

This is somewhat confusing since it reports errors from the viewpoint of the new methods when the compatibility problem in fact is "Overload in old version cannot be found in new version". IncompatibleResultTypeProblem and IncompatibleMethTypeProblem are basically more specific versions of that error that should be reported as one (for example: if there's only one overload, report whether result or parameter types have changed, if there are multiple overloads, just report that none of the overloads matches).

[dwijnand]

I'll try your strategy, and see how it reflects in the testsuite.