Default URL for emoji images should be always https

[ocean90]

The default URL is currently set_url_scheme( '//s.w.org/images/core/emoji/72x72/' ) but the CDN is SSL-only, so in case set_url_scheme() returns "http" the request gets redirected to "https". That's pretty bad for our little friends.

curl -I http://s.w.org/images/core/emoji/72x72/1f680.png
HTTP/1.1 301 Moved Permanently
Content-Type: text/html
Date: Fri, 08 Jan 2016 19:53:08 GMT
Location: https://s.w.org/images/core/emoji/72x72/1f680.png
Server: nginx
Content-Length: 178

It's seems like this was an oversight in [31938] because s0.wp.com has no such redirect.

h/t: @glueckpress – ​http://glueckpress.com/7295/schnellere-emoji-wordpress-plugin/

[johnbillion]

In 36249:

Emoji: Explictly use https as the scheme for emoji fallback images, as they're only served over HTTPS by the CDN anyway.

Fixes #35376
Props ocean90

[ocean90]

In 36428:

Emoji: Explicitly use https as the scheme for emoji fallback images, as they're only served over HTTPS by the CDN anyway.

Merges [36249] to the 4.4 branch.
See #35376.

[desrosj]

#33688 was marked as a duplicate.