Refactor extra generator registration to use factories

This will allow additional information about the availability
and capabilities of extra generators to be queried without
actually creating them.

Instead of a static NewFactory() method like the main generator
factories have, use a static GetFactory() method to get a pointer to a
statically allocated extra generator factory.  This simplifies memory
management.

Source/cmGlobalKdevelopGenerator.cxx

@@ -25,20 +25,28 @@
 #include <cmsys/FStream.hxx>
 #include <cmsys/SystemTools.hxx>
 
-void cmGlobalKdevelopGenerator::GetDocumentation(cmDocumentationEntry& entry,
-                                                 const std::string&) const
-{
-  entry.Name = this->GetName();
-  entry.Brief = "Generates KDevelop 3 project files.";
-}
-
 cmGlobalKdevelopGenerator::cmGlobalKdevelopGenerator()
   : cmExternalMakefileProjectGenerator()
 {
-  this->SupportedGlobalGenerators.push_back("Unix Makefiles");
+}
+
+cmExternalMakefileProjectGeneratorFactory*
+cmGlobalKdevelopGenerator::GetFactory()
+{
+  static cmExternalMakefileProjectGeneratorSimpleFactory<
+    cmGlobalKdevelopGenerator>
+    factory("KDevelop3", "Generates KDevelop 3 project files.");
+
+  if (factory.GetSupportedGlobalGenerators().empty()) {
+    factory.AddSupportedGlobalGenerator("Unix Makefiles");
 #ifdef CMAKE_USE_NINJA
-  this->SupportedGlobalGenerators.push_back("Ninja");
+    factory.AddSupportedGlobalGenerator("Ninja");
 #endif
+
+    factory.Aliases.push_back("KDevelop3");
+  }
+
+  return &factory;
 }
 
 void cmGlobalKdevelopGenerator::Generate()