Task-number: QTCREATORBUG-1358
Reviewed-by: Roberto Raggi

It seems that storing the TranslationUnit together with the Symbol
was a bad idea. Unfortunately, we release TranslationUnit(s) as
soon as we can, but we keep the Control around. So using the Control
is definitely safer.

Reviewed-by: Roberto Raggi

Fixes function argument list code completion not completing the cv
qualifier.

Regression from 9efa5d94.

Task-number: QTCREATORBUG-1037
Reviewed-by: Roberto Raggi

For example:
    template <typename ::foo::bar>...

Done by: Roberto Raggi
Reviewed-by: erikv

For example,
  template <template <typename> class X> struct foo {};

Reviewed-by: erikv