Use the same load options to get properties and to check resumability
Also remove isManualCall argument: we already have filtered HTTP referer in "own window" and we should always filter "invisible" (in UI) referer.
(#4)
Simplify code
(related to #4)
Remove lpp_canResumeDownload and lpp_resumeDownloadTested before new request
And provide "global" lpp_resumeDownloadTested
(#4)
Cancel resumable check in appropriate cases
(#4)