<rdar://problem/12493007>

Added a new API call to help efficiently determine if a SBValue could have children:

     bool
     SBValue::MightHaveChildren ();
     
This is inteneded to be used bui GUI programs that need to show if a SBValue needs a disclosure triangle when displaying a hierarchical type in a tree view without having to complete the type (by calling SBValue::GetNumChildren()) as completing the type is expensive.

llvm-svn: 166460