vnc: buffer code improvements, bugfixes.

# gpg: Signature made Mon 16 Nov 2015 17:20:02 GMT using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/kraxel/tags/pull-vnc-20151116-1:
  vnc: fix mismerge
  buffer: allow a buffer to shrink gracefully
  buffer: factor out buffer_adj_size
  buffer: factor out buffer_req_size
  vnc: recycle empty vs->output buffer
  vnc: fix local state init
  vnc: only alloc server surface with clients connected
  vnc: use vnc_{width,height} in vnc_set_area_dirty
  vnc: factor out vnc_update_server_surface
  vnc: add vnc_width+vnc_height helpers
  vnc: zap dead code
  vnc-jobs: move buffer reset, use new buffer move
  vnc: kill jobs queue buffer
  vnc: attach names to buffers
  buffer: add tracing
  buffer: add buffer_shrink
  buffer: add buffer_move
  buffer: add buffer_move_empty
  buffer: add buffer_init
  buffer: make the Buffer capacity increase in powers of two

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>