We add checks for various error cases that could combine to cause this problem.  While we
	never got a reproducible case, we are confident that this is the only file removal done
	in the download code, and its ability to wreak havoc has been clipped.

        Reviewed by Richard.

        * Downloads.subproj/WebDownloadHandler.m:
        (-[WebDownloadHandler cleanUpAfterFailure]):  Only nuke the partial download if in fact we created
	a new download file.  Never nuke a directory.
        (-[WebDownloadHandler createFileIfNecessary]):  Don't add "." to the foo-1 filenames we generate
	if the original filename doesn't have any extension.
        * WebView.subproj/WebMainResourceClient.m:
        (-[WebMainResourceClient continueAfterContentPolicy:response:]):
	If the policyDelegate gives us a nil filename, just stop the whole load, instead of trying to
	overwrite the user's home directory.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@3281 268f45cc-cd09-0410-ab3c-d52691b4dbfc