Downloading dynamic content does not work

[aleek]

Hi,

when downloading dynamic content with Request.SkipExisting = false and Request.NoResume = true, it does not get overwritten, if ContentLength of remote file does not equal local file size,
It can be fixed in two ways.

1. Add proper documentation to Request.SkipExisting, that if you download dynamically generated file, you should also set Request.NoResume to false
2. Add new variable to Request, that will set Request.SkipExisting to false and Request.NoResume to true

After discussion is done, I'll prepare pull request.

Regards
Alex