Include struct context info for parser/sema crashes. This

gives us:

Stack dump:
0.	using-directive.cpp:26:16: in compound statement ('{}')
1.	using-directive.cpp:26:16: parsing function body 'A::K1::foo'
2.	using-directive.cpp:25:3: parsing struct/union/class body 'A::K1'
3.	using-directive.cpp:5:1: parsing namespace 'A'
4.	clang using-directive.cpp 
Abort

for code like:

namespace A {
...
  class K1 {
    void foo() { <<crash>>

llvm-svn: 66124