labels_layer plugin is incompatible with minimap plugin

[cody-somerville]

labels_layer plugin ("CartoDB and default Ingress map with labels above Ingress layers") is incompatible with the IITC bundled minimap plugin ("Show a mini map on the corner of the map"). This is likely due to how labels_layer monkey patches but I didn't look very close.

Reporting issue for posterity / in case someone else runs into this.