fixed bug when pasting files in another path

remove the leading directory separator from the original name
before moving the file in the new location.

Based on FR commit: 25eea1c2b80200af7c166fa317bcefbc4874de7d
From: Paolo Bacchilega <paobac@src.gnome.org>
When canceling an operation kill all the sub-processes as well

create a new process group and kill the process group to stop the
operation.

Based on FR commit: baff9720f59d85d5118ca0220b7c680dc6964d30
From: Paolo Bacchilega <paobac@src.gnome.org>
make the progresss dialog modal when not in batch mode

Based on FR commit: 35ad1e2f8b9e2f8609fd663dd3138d482930d116
From: Paolo Bacchilega <paobac@src.gnome.org>
do not set the border width for any dialog

Based on FR commit: 2d1d283b71d4c5bf830ecc38a560df9b93932215
From: Paolo Bacchilega <paobac@src.gnome.org>
Gtk3: Silence the GtkBox and GtkPaned deprecation warnings