Description: Set default path in GTK file choosers to cwd

Author: أحمد المحمودي (Ahmed El-Mahmoudy) <aelmahmoudy@sabily.org>
Bug: https://bugs.launchpad.net/pcb/+bug/855621
Bug-Debian: http://bugs.debian.org/642060
Forwarded: https://bugs.launchpad.net/pcb/+bug/855621/+attachment/2436146/+files/default_GtkFileChooser_cwd.diff

Signed-off-by: Bert Timmerman <bert.timmerman@xs4all.nl>
Use gtk_file_chooser_set_filename() if we know a filename.