Method binding completion hides role methods

[mosconi]

Proposals for method bindings are not shown for methods that have the same name as existing role methods. For example, if you have an abstract role method, no proposal for a callout to a same-named base method is made. Same for callin methods.

[stephan]

Tests and implementation in r23196:

• if an abstract method exists all method binding kinds are proposed
• if a concrete method exists only a callin binding is proposed