cmCTestSVN: Fix compilation with Sun CC 5.1

Hack access to cmCTestVC::Revision on this compiler to avoid errors like

 Source/CTest/cmCTestSVN.cxx, line 23: Error: cmCTestSVN::SVNInfo is not accessible from cmCTestSVN::Revision.
 Source/CTest/cmCTestSVN.cxx, line 22: Error: cmCTestVC::Revision is not accessible from file level.

Source/CTest/cmCTestSVN.h

@@ -63,6 +63,7 @@ private:
 
   // Extended revision structure to include info about external it refers to.
   struct Revision;
+  friend struct Revision;
 
   // Info of all the repositories (root, externals and nested ones).
   std::list<SVNInfo> Repositories;

Source/CTest/cmCTestVC.h

@@ -67,6 +67,9 @@ protected:
   virtual void NoteNewRevision();
   virtual bool WriteXMLUpdates(std::ostream& xml);
 
+#if defined(__SUNPRO_CC) && __SUNPRO_CC <= 0x510
+public: // Sun CC 5.1 needs help to allow cmCTestSVN::Revision to see this
+#endif
   /** Basic information about one revision of a tree or file.  */
   struct Revision
   {
@@ -80,6 +83,7 @@ protected:
     std::string Log;
   };
 
+protected:
   struct File;
   friend struct File;