bug#9054: 24.0.50; show source in other window

[Juri Linkov]

>>> The back-end should return collected data as alist,
>>> and front-end should render data as the buffer text.
>>
>> Hmmm...  I still don't get it.
>
> For example, ‘C-h f’ (describe-function) first calls a back-end function
> that collects all information about a function and returns it in a such form:
>
>   ((type . function)
>    (name . "car")
>    (source-file . "src/data.c")
>    (Info-node . "(elisp) List Elements")
>    (docstring . ...)
>    ...)

And when some data collection is too time-consuming
it could return it as lambda for lazy evaluation. e.g.:

  ((type . function)
   (name . "car")
   (references . (lambda () (collect-references "car")))
   ...)