Disable undo in PDF buffer.

* lisp/pdf-view.el (pdf-view-mode): Call buffer-disable-undo.
Documentation typo.
Avoid errors when killing Emacs.

* lisp/pdf-info.el (kill-emacs-hook): Let Emacs kill the process.
Make pdf-tools compatible with Emacs 24.3

* lisp/pdf-view.el (pdf-view-mode): Set major-mode before setting up winprops.
  (pdf-view-new-window-function): Check winprops for image.
  (pdf-view-desired-image-size): Use compatibility macro
  pdf-util-window-pixel-width.

* lisp/pdf-util.el: (pdf-util-window-pixel-width): Compatibility macro
  for window-width in pixel.

  (image-mode-winprops): Use implementation from 24.4 if current
  buffer is in pdf-view-mode.

* lisp/pdf-annot.el (pdf-annot-print-annotation-latex): Don't use
  org-create-formula-image, since it is not available in 24.3.

* README.org: Qualify needed Emacs version to be 24.3