fr-window: fix crash on _fr_window_ask_overwrite_dialog() function

Don't immediatly unref 'destination' after passing it to
g_file_query_info_async() , instead unref it from within the callback
for the aforementioned function when it's done with it.
dnd: don't use a fake name when communicating the xds dragged file

Use the real name, as the target application may need it (eg.
nautilus for revealing it, or gedit to open it).

Part of bug 710546
fixed code style
fr-window: Improve XDS dnd support

Improve file-roller XDS dnd support by sending the 'success'
response only after the file(s) has already been extracted, so
the target dnd application can operate on it (eg. gedit may
want to open it, nautilus may want to reveal it).

The XDS spec states that when sending the success ('S') response, the
file should have already been written to disk, but assumed this would
be done in a synchronous (and thus blocking) operation, asynchronous
(callback based) apis were not common when the XDS spec was done so
that's probably the reason.

So as file-roller does, in a right manner, its file operations asynchronously,
thats probably why it didn't care to send the success response at the right time.

This patch workarounds the XDS spec limitation and makes file-roller to wait
for the async operations to complete before sending the success response.

It does so, without blocking the main ui thread, by creating and using a GMainLoop
the same way as it's done by the gtk_dialog_run() call, which shows a dialog and
waits for its response without blocking the ui.

Fixes bug 710546
declare some functions as static + indentation
fixed dnd from the folder tree