view-dnd: pass the correct attrs number to pango_get_log_attrs()

num_attrs always needs to be the number of characters plus one, or Pango
will warn and possibly corrupt memory.

https://bugzilla.gnome.org/show_bug.cgi?id=706131
file-operations: replace control characters for FAT fs operations

Those are invalid - if we find one, replace it with an underscore as
well.

https://bugzilla.gnome.org/show_bug.cgi?id=706131
file operations: fix double unref and show invalid filename error dialog

Remove a superflous g_object_unref() call plus show error dialog when
creating a new file with an invalid file name for the destination
file system.

Fixes bug 706131

https://bugzilla.gnome.org/show_bug.cgi?id=706131