on all example and debug pages (i.e. 30 HTML files), so that on `github.io`, there is no "mixed content" warning anymore.
Switch Leaflet CDN from cdnjs to "official" unpkg.com.
Switch `leaflet.js` to `leaflet-src.js` (14 files).
Also updated the copyright link to OSM using the "official" URL (with https), even though it takes more bytes than the shortcut URL. But at least it is easier for visitors to understand the relationship between the link text and the URL.
for compatibility with Leaflet 1.0.
Updated all example pages with correct CDN link to Leaflet 1.0.0-beta.2 assets.
Corrected MarkerCluster.Spidefier to avoid trying to setOpacity and setZindexOffset on L.Circle (these can be clustered and spiderfied, but they do not have those methods).
All tests should pass now and Leaflet-master could be updated.
