Python commands:

 It is now possible to use 'command alias --python' to define a command name that actually triggers execution of a Python function
 (e.g. command alias --python foo foo_impl makes a command named 'foo' that runs Python function 'foo_impl')
 The Python function foo_impl should have as signature: def foo_impl(debugger, args, stream, dict): where
  debugger is an object wrapping an LLDB SBDebugger
  args is the command line arguments, as an unparsed Python string
  stream is an SBStream that represents the standard output
  dict is an internal utility parameter and should be left untouched
 The function should return None on no error, or an error string to describe any problems

llvm-svn: 137722