C++2011: inline namespaces

[David Nolden]

- This could be solved by adding "automatic" namespace-imports
(AliasDeclaration) right behind inline namespace declarations. An
additional lookup would be required to match specialized declarations
to their base (where only inline namespace imports would be valid).

- Another solution would be simply ignoring inline namespaces (don't
create contexts for them). After all they just seem to be a very ugly
implementation detail required to prevent linking problems. I think
this would be the best solution.