printing: Don't leak http connection to CUPS

Close http connection to CUPS after execution
of request which created it.

https://bugzilla.gnome.org/show_bug.cgi?id=720535
cell-renderer: Check for NULL return in vfunc start_editing()

This virtual function may return NULL, so, let's check if that's
the case and exit the function apropriately.

https://bugzilla.gnome.org/show_bug.cgi?id=720554
GtkPlacesSidebar: avoid a crash

Be more careful when comparing uris during DND - they may
be NULL.

https://bugzilla.gnome.org/show_bug.cgi?id=720264
GtkPlacesSidebar: Don't show desktop if its home

We go to extra length to set the desktop_uri to NULL when
desktop == home, but then we were adding the (non-functional)
place item anyway. Don't do that.
Updated Russian translation
Updated Greek translation
Set an accessible name on menu buttons

These commonly have just an image in them, so lets at least
call them 'Menu'.
Add a menubutton to the a11y tests
Improve menubutton a11y

The button now claims its menu as a child for a11y purposes,
which makes it possible for ATs to see it when the navigate
the tree top-down.

Update the a11y test to match.
Allow close buttons on dialogs

It was a long-standing problem for some users of GtkDialog that
there is no guaranted way to close it. So, lets show a close
button.
Fix a few warnings
Redo header bar decorations once more

Applications need a way to fix or adapt the decoration layout,
for situations like split header bars. Setting the layout from
the theme with a style property did not offer a good way to do
this, and the ::show-close-button property does not provide
fine-grained control.

To improve the situation, move the layout string to a property of
GtkHeaderBar which is backed by a setting. This allows platforms to
set a default button layout independent of the theme, while applications
can override the default.

The style GtkWindow style property is now deprecated and ignored.