IDE completion should know about renaming imports.

[odersky]

Say you have

import java.util.{List => JList}

Then scope completion with J should give JList. Right now it cannot to that because we return lists of symbols from completion requests, and List is clearly not a valid completion.

For the moment, renamed imports are simply ignored. To fix this, it would be good to first have some tests for completion requests.

[Duhemm]

There's a fix for that in #4977