RemoteError._render_traceback_ calls self.render_traceback...
RemoteError._render_traceback_ calls self.render_traceback
rather than an alias
There are two options here:
1. `_render_traceback_` should *call* render_traceback
2. any subclass that redefines render_traceback must also redefine `_render_traceback_`
I went with 1., which is more efficient code-wise when subclassing RemoteError
(would prevent future cases of this same mistake),
but less efficient execution-wise, because it involves an extra function call.
closes
#2303
