Xpra: Ticket #934: Pillow errors with Ubuntu Vivid

Found on an up to date vivid 64-bit system:

2015-07-30 13:37:42,939 PIL_encode((314, 283, 'webp', '355448 bytes', 'RGBA', 1256)) converting to RGBA failed
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/xpra/codecs/pillow/encode.py", line 69, in encode
    im = PIL.Image.frombuffer(rgb, (w, h), pixels, "raw", pixel_format, image.get_rowstride())
  File "/usr/lib/python2.7/dist-packages/PIL/Image.py", line 2119, in frombuffer
    core.map_buffer(data, size, decoder_name, None, 0, args)
TypeError: must be sequence of length 3, not 2

and

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/xpra/server/source.py", line 1837, in encode_loop
    fn_and_args[0](*fn_and_args[1:])
  File "/usr/lib/python2.7/dist-packages/xpra/server/window_source.py", line 1320, in make_data_packet_cb
    packet = self.make_data_packet(damage_time, process_damage_time, wid, image, coding, sequence, options, flush)
  File "/usr/lib/python2.7/dist-packages/xpra/server/window_source.py", line 1669, in make_data_packet
    ret = encoder(coding, image, options)
  File "/usr/lib/python2.7/dist-packages/xpra/server/window_source.py", line 1752, in webp_encode
    return webp_encode(coding, image, self.rgb_formats, self.supports_transparency, q, s, options)
  File "/usr/lib/python2.7/dist-packages/xpra/server/picture_encode.py", line 72, in webp_encode
    return enc_pillow.encode(x, image, quality, speed, supports_transparency)
  File "/usr/lib/python2.7/dist-packages/xpra/codecs/pillow/encode.py", line 69, in encode
    im = PIL.Image.frombuffer(rgb, (w, h), pixels, "raw", pixel_format, image.get_rowstride())
  File "/usr/lib/python2.7/dist-packages/PIL/Image.py", line 2119, in frombuffer
    core.map_buffer(data, size, decoder_name, None, 0, args)
TypeError: must be sequence of length 3, not 2

and

2015-07-30 18:48:53,010 draw error
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/xpra/client/ui_client_base.py", line 2054, in _do_draw
    window.draw_region(x, y, width, height, coding, data, rowstride, packet_sequence, options, [record_decode_time])
  File "/usr/lib/python2.7/dist-packages/xpra/client/client_window_base.py", line 462, in draw_region
    self._backing.draw_region(x, y, width, height, coding, img_data, rowstride, options, callbacks)
  File "/usr/lib/python2.7/dist-packages/xpra/client/window_backing_base.py", line 488, in draw_region
    self.paint_webp(img_data, x, y, width, height, options, callbacks)
  File "/usr/lib/python2.7/dist-packages/xpra/client/window_backing_base.py", line 245, in paint_webp
    buffer_wrapper, width, height, stride, has_alpha, rgb_format = dec_webp.decompress(img_data, has_alpha, options.get("rgb_format"))
AttributeError: 'NoneType' object has no attribute 'decompress'

and

2015-07-30 18:48:54,669 gtk2.GLWindowBacking(1, (499, 316), YUV444P).gl_paint_planar(..) error: ("No array-type handler for type <type 'memoryview'> (value: <memory at 0x7f6a000d20e8>) registered", <OpenGL.GL.images.ImageInputConverter object at 0x7f6a028480d0>)
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/xpra/client/gl/gl_window_backing_base.py", line 695, in gl_paint_planar
    self.update_planar_textures(x, y, enc_width, enc_height, img, pixel_format, scaling=(enc_width!=width or enc_height!=height))
  File "/usr/lib/python2.7/dist-packages/xpra/client/gl/gl_window_backing_base.py", line 749, in update_planar_textures
    glTexSubImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, 0, 0, width//div_w, height//div_h, GL_LUMINANCE, GL_UNSIGNED_BYTE, pixel_data)
  File "/usr/lib/python2.7/dist-packages/OpenGL/latebind.py", line 45, in __call__
    return self._finalCall( *args, **named )
  File "/usr/lib/python2.7/dist-packages/OpenGL/wrapper.py", line 782, in wrapperCall
    pyArgs = tuple( calculate_pyArgs( args ))
  File "/usr/lib/python2.7/dist-packages/OpenGL/wrapper.py", line 355, in calculate_pyArgs
    yield converter(args[index], self, args)
  File "/usr/lib/python2.7/dist-packages/OpenGL/GL/images.py", line 400, in __call__
    return arrayType.asArray( arg )
  File "/usr/lib/python2.7/dist-packages/OpenGL/arrays/arraydatatype.py", line 141, in asArray
    return cls.getHandler(value).asArray( value, typeCode or cls.typeConstant )
  File "/usr/lib/python2.7/dist-packages/OpenGL/arrays/arraydatatype.py", line 52, in __call__
    typ, repr(value)[:50]