Fix serialization of Python breakpoint commands.

Fix serialization of Python breakpoint commands.

CommandData breakpoint commands didn't know whether they were
Python or Command line commands, so they couldn't serialize &
deserialize themselves properly.  Fix that.
I also changed the "breakpoint list" command to note in the output
when the commands are Python commands.  Fortunately only one test
was relying on this explicit bit of text output.

llvm-svn: 282432