Fix classification of externals in svn status

CTest runs 'svn status' to identify modified and conflicting files in
the working directory.  This commit fixes the interpretation of the 'X'
status, which corresponds to svn eXternals.  This status should be
ignored rather than treated as a local modification.

Source/CTest/cmCTestSVN.cxx

@@ -423,13 +423,13 @@ private:
     // See "svn help status".
     switch(status)
       {
-      case 'M': case '!': case 'A': case 'D': case 'R': case 'X':
+      case 'M': case '!': case 'A': case 'D': case 'R':
         this->SVN->DoModification(PathModified, path);
         break;
       case 'C': case '~':
         this->SVN->DoModification(PathConflicting, path);
         break;
-      case 'I': case '?': case ' ': default:
+      case 'X': case 'I': case '?': case ' ': default:
         break;
       }
     }