wrong legend symbols when using handles and labels from get_legend_handles_labels

Hello, when I try to use `get_legend_handles_labels` and use these handles and labels in the legend, I get wrong results for `errobar` plots with actual errors.

this works fine:

```julia
errorbar([1],[2],label = "no error")
errorbar([2],[2],[3],label = "with error")
legend()
```

while this one produces a wrong result:

```julia
errorbar([1],[2],label = "no error")
errorbar([2],[2],[3],label = "with error")
h, l = gca()[:get_legend_handles_labels]()
legend(h,l)
```

I cannot tell you where the problem lies but I hope this can be fixed or there is a workaround... Thanks.

Reproduce the two Julia examples using errorbar, get_legend_handles_labels, and legend(h,l), then compare the resulting legend symbols. Start by tracing the get_legend_handles_labels and legend entry points in PyPlot.jl and how they pass handles to matplotlib. Done means the explicit-handle form produces the same correct symbols as the direct legend() call, or a documented workaround is provided.

Scritto dal modello di indicizzazione a partire dal testo della issue.