Fixed a bug regarding tablist columns.

* lisp/tablist.el (tablist-current-column): Compute the current column
  in a more sane and hopefully correct way.  Extended documentation.
Use a variable for saving a function definition.

* lisp/pdf-util.el: Using defalias is asking for trouble, better use defvar.
Round scroll values.

* lisp/pdf-util.el (pdf-util-required-hscroll): Round return value.
  (pdf-util-required-vscroll): Dito.
Fix documentation.
Handle display properties when bookmarking.

* lisp/pdf-view.el (pdf-view-bookmark-make-record): Store the slice,
size and image-origin in the bookmark.
(pdf-view-bookmark-jump): Restore above values.

* lisp/pdf-util.el (pdf-util-image-displayed-edges): Round the return
  value. Added a displayed-p argument.