reapply my patch for PR4451, which improves diagnostics for :: vs : confusion.
This time with a fix to bail out when in a dependent context.

llvm-svn: 90730
diff --git a/clang/test/SemaCXX/nested-name-spec.cpp b/clang/test/SemaCXX/nested-name-spec.cpp
index 83c7241..6a51261 100644
--- a/clang/test/SemaCXX/nested-name-spec.cpp
+++ b/clang/test/SemaCXX/nested-name-spec.cpp
@@ -186,12 +186,10 @@
 };
 
 
-// PR4452
-// FIXME: This error recovery sucks.
-foo<somens:a> a2;  // expected-error {{unexpected namespace name 'somens': expected expression}} \
-expected-error {{C++ requires a type specifier for all declarations}}
+// PR4452 / PR4451
+foo<somens:a> a2;  // expected-error {{unexpected ':' in nested name specifier}}
 
-somens::a a3 = a2;
+somens::a a3 = a2; // expected-error {{cannot initialize 'a3' with an lvalue of type 'foo<somens::a>'}}