Leaflet-pip is not working with Leaflet-draw plugin

Nobody has claimed this yet.

Hello,
I've tried to update my app with leaflet 1.0.x and I'm facing up to an incompatibility between 2 plugins:
- [leaflet-draw](https://github.com/Leaflet/Leaflet.draw)
- leaflet-pip

Since [this commit in leaflet-pip](https://github.com/mapbox/leaflet-pip/commit/e76cfdc064cfe3d29ab01eebe2d4ad9b35564129#diff-168726dbe96b3ce427e7fedce31bb0bcR28), function `is_poly` is not anymore able to take into account polygons just created with leaflet-draw. I thought leaflet-draw created an incorrect polygon in [this issue](https://github.com/Leaflet/Leaflet.draw/issues/731) but I suspect now leaflet-pip is maybe not enough permissive.
I would suggest a PR which updates the `is_poly` function from your plugin:
```
function isPoly(l) {
if (l instanceof L.Polygon) return true;
return l.feature && l.feature.geometry && l.feature.geometry.type &&
['Polygon', 'MultiPolygon'].indexOf(l.feature.geometry.type) !== -1;
}
```
Indeed layer created by leaflet-draw has no `l.feature && l.feature.geometry && l.feature.geometry.type` attribute...

And maybe rollback entirely https://github.com/mapbox/leaflet-pip/commit/ff2b2f43df3d4a539afb587e7fe033046f6e3b7f for `is_poly`:
```
function isPoly(l) {
return L.MultiPolygon && l instanceof L.MultiPolygon ||
l instanceof L.Polygon ||
l.feature && l.feature.geometry && l.feature.geometry.type &&
['Polygon', 'MultiPolygon'].indexOf(l.feature.geometry.type) !== -1;
}
```

What do you thinking about it ?

Fabien

Start at the isPoly function in leaflet-pip and compare its current layer checks with the Leaflet-draw layers described here. Reproduce the incompatibility with Leaflet 1.0.x and leaflet-draw, then verify that newly drawn polygons are recognized without breaking GeoJSON Polygon or MultiPolygon handling.

Written by the indexing model from the issue text.