Correct collections variable definitions to avoid many scaladoc warnings.

Running 'ant docs.lib' produces such a long warning list that nobody seems to care. Consequently the documentation for stdlib contains many errorneous signatures.

This PR addresses most of the "Unresolved $Coll when documenting XXX" warnings and reduces scaladoc output from 1600 to 400 lines. Since this is a pure documentation change, it is safe to merge in 2.11.x