bug#20148: 24.4: function `bookmark-get-bookmark'

[Drew Adams <drew.adams@oracle.com>]

> Function `bookmark-get-bookmark' ...
> 
> 1] tests for the existence of a bookmark by checking whether the input
> string matches a cons cell. This casts a net much wider than desirable,
> and might better be (assoc bookmark-name-or-record bookmark-alist).

See the actual code.

> 2] returns only a string value on error, without passing nil back to the
> calling function.
> 
> My usage case is that I was scripting a function to find org-mode files
> in a directory tree, and add them to a bookmark list if they aren't
> already bookmarked according to my naming convention. Originally, I had
> tried checking for the existence of a bookmark using a few of the
> bookmark.el functions, such as bookmark-get-bookmark, but that looked
> inconvenient because they returned string values on failure.

See the actual code.

The doc string neglects to mention the optional argument.  It should
say something like this (taken from Bookmark+):

  Non-nil optional arg NOERROR means return nil if BOOKMARK is not a
  valid bookmark.  If NOERROR is nil then raise an error in this case.