Syntax to refer to a specific overload of a function

```
pragma experimental "v0.5.0";

contract Selector {
function transfer(address, uint) external;
function transfer(address) external;
function calculateSelector() public pure returns (bytes4) {
return this.transfer.selector;
}
}
```

Not sure what could be a good notation and/or a generic way for this. As a workaround a function type can be defined.

Split off #3544.

EDIT by @cameel: Renamed the issue since we often defer to it as the main issue about resolving ambiguous overloads. The original title was `Support retrieving selector of an overloaded function`.

No source file or test is named. Start with the overloaded transfer declarations and the this.transfer.selector expression, then review the discussion and linked issue #3544 for any agreed notation or constraints. Done means the ambiguity has a defined resolution and is covered by compiler tests.

Written by the indexing model from the issue text.