I am in a dead end :(
http://code.google.com/p/android/issues/detail?id=1978
The browser needs to hit the server to determine that something is a download, and than the download manager has to separately contact the server for downloading.
So, Android fire up first request to open dialogue box for "are you sure? - yes/no". And if user click "Yes" Android Forward request to Android DownloadManager and manager send second request to download file. (some Android version send request to DownloadManager immediately)
The problem is that both request, first and second, are type of GET (not HEAD).