Stop trying to analyze class-hierarchies for dependently-scoped id-expressions;

there's nothing interesting we can say now that we're correctly not requiring
the qualifier to name a known base class in dependent contexts.

Require scope specifiers on member access expressions to name complete types
if they're not dependent;  delay lookup when they are dependent.

Use more appropriate diagnostics when qualified implicit member access
expressions find declarations from unrelated classes.

llvm-svn: 90289