Use HTTPS for Bing services and tiles when the document is HTTPS.

A new option "tileProtocol" can be used to force the protocol.
Merge remote-tracking branch 'origin/master' into bingHttps
Update CHANGES.
Merge remote-tracking branch 'origin/master' into bingHttps
Merge pull request #1443 from AnalyticalGraphicsInc/bingHttps

Use HTTPS for Bing services and tiles when the document is HTTPS.