1901 - Fix Welcome Page

Solution was very simple to implement, no content disposition header was
necessary.
Tested with both Firefox and Chrome, using binary image file stored in
folder, as well as with text data using LIT cap.

src/allmydata/web/welcome.xhtml

@@ -59,6 +59,7 @@
                   Filename
                   <input type="text" name="filename" />
                 </label>
+                <input type="hidden" name="save" value="true"/>
                 <p><input type="submit" class="btn" value="Download File &#187;" /></p>
               </form>
             </div>