Fix up various corner case problems.

Fix up various corner case problems.
* doc-view.el (doc-view-last-page-number): New function.
(doc-view-mode, doc-view-last-page, doc-view-goto-page): Use it.
(doc-view-goto-page): Avoid inf-loops when the conversion fails.
(doc-view-kill-proc): Avoid inf-loop in freak cases.
(doc-view-reconvert-doc): Use the new recursive delete-directory.
(doc-view-convert-current-doc): Don't create the resolution.el file
here any more.
(doc-view-pdf/ps->png): Do it here instead.
(doc-view-already-converted-p): Check that resolution.el is present.
(doc-view-pdf->png): Don't rely on doc-view-pdf/ps->png for the few
windows that are not yet showing images.