Update the comment to clarify that libxl_sigchld_owner_libxl_always
implies having only one libxl_ctx, and that
libxl_sigchld_owner_mainloop requires one call to
libxl_childproc_exited per ctx.
Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>