Example editing: Allow multiple editing buffers

Example editing: Allow multiple editing buffers

Hsiu-Khuern Tang writes:

> Hi Carsten,
>
> You recently changed org-edit-src-code to use a separate buffer
> instead of an indirect buffer.  One side effect of this is that I
> can no longer edit several code examples at the same time:
> opening the second buffer will silently discard any changes made
> in the first.  I would prefer this behavior: when opening the
> second edit source buffer, write any changes in the first buffer
> to the originating Org buffer (but don't save it, of course).
>
> Another approach is to use different buffer names.

The better approach is clearly to allow several buffers, now
implemented with this commit.