Check for suggested_filename in opts table

If the opts table contains a key suggested_filename,
it will override the one that webkit would provide
based on uri and headers. The suggested file name will
be passed down to signals for further processing, just
like the one webkit suggests.

lib/downloads.lua

@@ -122,7 +122,7 @@ function add(uri, opts)
 
     -- Emit signal to get initial download location
     local fn = _M.emit_signal("download-location", d.uri,
-        d.suggested_filename, d.mime_type)
+        opts.suggested_filename or d.suggested_filename, d.mime_type)
 
     assert(fn == nil or type(fn) == "string" and #fn > 1,
         string.format("invalid filename: %q", tostring(file)))