Change the way command aliases are stored. Go from a model where a map holds...

Change the way command aliases are stored. Go from a model where a map holds the alias -> underlying command binding and another map holds the alias -> options, to a model where one single map holds the alias -> (all useful data) combination

Right now, obviously, this is just the pair of (CommandObjectSP,OptionArgVectorSP), so NFC

This is step one of a larger - and tricky - refactoring which will turn command aliases into interesting objects instead of passive storage that the command interpreter does smart things to
This refactoring, in turn, will allow us to do interesting things with aliases, such as intelligent and customizable help

llvm-svn: 262900