GtkFileChooser: Don't fill location_entry if we just populated the file list

Only fill the location entry with the file name of the tree view's
selected file when the selection was done by the user.

When the file chooser's action is GTK_FILE_CHOOSER_ACTION_OPEN, it
selects the first file in the tree view once loading has finished. For
this case we don't want it to insert the file name in the location
entry, as it hinders efficient navigation using the location entry. To
achieve this, use a priv flag to keep track of whether the
selection-changed signal was caused by the file chooser itself.

https://bugzilla.gnome.org/show_bug.cgi?id=386569
clipboard: Don't crash when data is requested from NULL window

This could happen if data was requested from a separate screen now that
multi-screen is no longer supported.

Ideally, we'd want to support copying to other screens, but that
requires solving in GDK as that's X-specific so cannot be well
abstracted by GDK (without the reintroduction of multiple screens).

https://bugzilla.gnome.org/show_bug.cgi?id=719314
GtkStyleContext: Invalidate contexts with a path

Fixes a tiny typo in commit f51c9d4154ba1ce4f20f7c4b7f705fe2756cb8ab
which manifested itself in GtkSpinButton's panels being drawn with an
incorrect, not updated state.

This patch took me more hours than you might think! :P

https://bugzilla.gnome.org/show_bug.cgi?id=709491