gdk3 gdk.h/gtk.h enums wrong values

Most of the enums defined in gtk-3.0/gdk/gdk.h have fields given
explicit values in the upstream, but have no values in the LSB version
(note the LSB gtk-2.0 ones do get assigned values). In some cases
this may be harmless but in some cases there are clear errors. These
enums all need to be examined and fixed up. Here's a partial example,
a hand-crafted bit of code to print out the first entries from
GdkEventType:

Native build:
  GDK_NOTHING = -1
  GDK_DELETE = 0
  GDK_DESTROY = 1
  GDK_EXPOSE = 2
  GDK_MOTION_NOTIFY = 3
  GDK_BUTTON_PRESS = 4
  GDK_2BUTTON_PRESS = 5
  GDK_DOUBLE_BUTTON_PRESS = 5
  GDK_3BUTTON_PRESS = 6
  GDK_TRIPLE_BUTTON_PRESS = 6
  GDK_BUTTON_RELEASE = 7
  GDK_KEY_PRESS = 8
  GDK_KEY_RELEASE = 9
  GDK_ENTER_NOTIFY = 10
  GDK_LEAVE_NOTIFY = 11

LSBCC build:
  GDK_NOTHING = 0
  GDK_DELETE = 1
  GDK_DESTROY = 2
  GDK_EXPOSE = 3
  GDK_MOTION_NOTIFY = 4
  GDK_BUTTON_PRESS = 5
  GDK_2BUTTON_PRESS = 6
  GDK_DOUBLE_BUTTON_PRESS = 7
  GDK_3BUTTON_PRESS = 8
  GDK_TRIPLE_BUTTON_PRESS = 9
  GDK_BUTTON_RELEASE = 10
  GDK_KEY_PRESS = 11
  GDK_KEY_RELEASE = 12
  GDK_ENTER_NOTIFY = 13
  GDK_LEAVE_NOTIFY = 14

notice by not giving values, we've missed the -1 for GDK_NOTHING,
which instead starts at the default 0; and the import also missed that
GDK_DOUBLE_BUTTON_PRESS and GDK_TRIPLE_BUTTON_PRESS are aliases and
don't take distinct values. They're defined as follows in the upstream
header:

  GDK_2BUTTON_PRESS = 5,
  GDK_DOUBLE_BUTTON_PRESS = GDK_2BUTTON_PRESS,
  GDK_3BUTTON_PRESS = 6,
  GDK_TRIPLE_BUTTON_PRESS = GDK_3BUTTON_PRESS,