Escape double quotes in URL passed to browse-url

* lisp/org.el (org-link-escape-chars-browser): Add char double quote.
* lisp/org.el (org-open-at-point): Make use of the constant
`org-link-escape-chars-browser'.
* testing/lisp/test-org.el
(test-org/org-link-unescape-ascii-extended-char): Fill paragraph.
(test-org/org-link-escape-url-with-escaped-char): Fill paragraph and
typo.
(test-org/org-link-escape-chars-browser): New test.

This is to make work to open the Org link
[[http://some.host.com/search?q="Org mode"]] in a browser.