Changes to Python commands:

 - They now have an SBCommandReturnObject instead of an SBStream as third argument
 - The class CommandObjectPythonFunction has been merged into CommandObjectCommands.cpp
 - The command to manage them is now:
  command script with subcommands add, list, delete, clear
   command alias is returned to its previous functionality
 - Python commands are now part of an user dictionary, instead of being seen as aliases
 

llvm-svn: 137785