Make it possible to use Forever Frame when requested.

- Instead of failing due to window.EventSource is supported, a log message sent that better transport methods are available.
This pull should close #1057

Changed back to the initial check of window.EventSource, but with different log message
Changed log message for not supporting FF when SSE is supported.
Merge pull request #2849 from DNIDNL/bug-1057

Change log message when Forever Frame is skipped in browsers that support SSE.