If browse-url-browser-function is an unknown symbol the error from
browse-url isn't very helpful.  Eg.

    M-: (setq browse-url-browser-function 'FOOBAR-browse-url)
    M-x browse-url http://www.gnu.org

    => Wrong type argument: listp, FOOBAR-browse-url

I hoped it would say the problem is the symbol is unbound, not that it's
supposed to be a list.  (The value can be a list of course, but if the
value is a symbol then it's surely meant to be the name of a function.)
Sending symbols down the `apply' leg of `browse-url' would give

    => Symbol's function definition is void: FOOBAR-browse-url

which I think is a much better.


2009-09-23  Kevin Ryde  <user42@zip.com.au>

	* net/browse-url.el (browse-url): Pass any symbol in
	browse-url-browser-function to `apply', since if you've mistakenly
	put an unbound symbol then the error from apply is much clearer
	that the function you wanted is not available.