ENH: Each cmake command now adds a cmake variable of its own name, set

to ON.  This allows constructs in CMakeLists.txt files like:
IF(FOO_COMMAND)
  FOO_COMMAND()
ENDIF(FOO_COMMAND)
This provides the option to add CMake commands for extra functionality
without breaking compatability with earlier versions of CMake.

Source/cmMakefile.cxx

@@ -390,6 +390,7 @@ void cmMakefile::AddCommand(cmCommand* wg)
 {
   std::string name = wg->GetName();
   m_Commands.insert( RegisteredCommandsMap::value_type(name, wg));
+  this->AddDefinition(name.c_str(), true);
 }
 
   // Set the make file