This commit leaves "b" aliased to the old _regexp-break for now. The two
variants are identical except that `_regexp-break` allows you to say:
`(lldb) b <unrecognized_input>
`
which gets translated to:
`break set <unrecognized_input>
`
So switching people to `_regexp-break-add` would be a surprising
behavior change. It would be wrong for `_regexp_break-add` have one
branch that call `break set`, so to avoid surprise, I'll add the command
and let people who are playing with `break add` instead of `break set`
can set the alias to the new one by hand for now.
6dafa096f4