Add a :print_module directive to the REPL.

This is basically the same as doing a :print_decl on every decl in the module,
except that it does not print extensions that come from other modules, and
/does/ print extensions and operators that come from this module.

Does not yet work for Clang modules or the Builtin module.

Swift SVN r7601

include/swift/Serialization/SerializedModuleLoader.h

@@ -110,6 +110,9 @@ public:
 
   virtual void getLinkLibraries(const Module *module,
                                 Module::LinkLibraryCallback callback) override;
+  
+  virtual void getDisplayDecls(const Module *module,
+                               SmallVectorImpl<Decl*> &results) override;
 };
 
 } // end namespace swift