Fix anonymous assistants

GtkAssistant supports not showing the sidebar with the page
titles (if the page have no titles). Unfortunately, we were
hiding the sidebar in this case, but still rendering the frame
behind it, leading to a broken appearance.
MSVC Builds: Fix Build of Introspection Files

We need to copy the GDK .lib/.dll from Release_Broadway\<Platform>\bin
or Debug_Broadway\<Platform>\bin to Release\<Platform>\bin or
Debug\<Platform>\bin respectively during the build of Broadway flavors of
GDK, as the MSVC introspection builds expects the GDK .lib/.dll to be
in Release\<Platform>\bin or Debug\<Platform>\bin.

Use a new property sheet to do so for Broadway builds of GDK-during the
builds of Win32-only GDK, the broadway builds of the GDK .lib/.dll would
be cleared out prior to the build of the Win32-only GDK.
revealer: clamp minimum size to natural one

Instead of just setting them equal.

https://bugzilla.gnome.org/show_bug.cgi?id=706938
gtkwindow: Consistently set the style classes for window-frame

In one place, we forgot to remove the BACKGROUND style class before
adding window-frame. Add a helper method so these are all the same.

https://bugzilla.gnome.org/show_bug.cgi?id=706922
gdk: Add opaque region setters

https://bugzilla.gnome.org/show_bug.cgi?id=706922
gtkwindow: Calculate the opaque window based off of the style

https://bugzilla.gnome.org/show_bug.cgi?id=706922
Fix a regression in GtkAssistant child property handling

GtkAssistant is bending the rules about child properties
of non-direct children, and the recent fix to accomodate
GtkInfoBar changes broke things. The effect was that child
properties of assistant pages in ui files were just not
applied, so all pages ended up without titles and with
the normal page type, leading to broken assistants all
over the place.

https://bugzilla.gnome.org/show_bug.cgi?id=706756