bug#9082: Add hints to documentation of car and cdr for (e)lisp newcomers

[Adam Sjøgren]

** Description

Adds hints to the documentation of car and cdr to help newbies remember
which is which.

Saying that (car|cdr) returns the (car|cdr) of a LIST is a little terse
for beginners (probably the only ones looking at the documentation of
such basic functions).

** ChangeLog

2011-07-14  Adam Sjøgren  <asjo@koldfront.dk>

        * data.c (car, cdr): add functionality hints to documentation.

** Patch

=== modified file 'src/data.c'
*** src/data.c  2011-07-10 08:20:10 +0000
--- src/data.c  2011-07-14 13:23:02 +0000
*************** DEFUN ("floatp", Ffloatp, Sfloatp, 1, 1,
*** 463,469 ****
  /* Extract and set components of lists */
  
  DEFUN ("car", Fcar, Scar, 1, 1, 0,
!        doc: /* Return the car of LIST.  If arg is nil, return nil.
  Error if arg is not nil and not a cons cell.  See also `car-safe'.
  
  See Info node `(elisp)Cons Cells' for a discussion of related basic
--- 463,469 ----
  /* Extract and set components of lists */
  
  DEFUN ("car", Fcar, Scar, 1, 1, 0,
!        doc: /* Return the car (first element) of LIST.  If arg is nil, return 
nil.
  Error if arg is not nil and not a cons cell.  See also `car-safe'.
  
  See Info node `(elisp)Cons Cells' for a discussion of related basic
*************** DEFUN ("car-safe", Fcar_safe, Scar_safe,
*** 481,487 ****
  }
  
  DEFUN ("cdr", Fcdr, Scdr, 1, 1, 0,
!        doc: /* Return the cdr of LIST.  If arg is nil, return nil.
  Error if arg is not nil and not a cons cell.  See also `cdr-safe'.
  
  See Info node `(elisp)Cons Cells' for a discussion of related basic
--- 481,487 ----
  }
  
  DEFUN ("cdr", Fcdr, Scdr, 1, 1, 0,
!        doc: /* Return the cdr (rest) of LIST.  If arg is nil, return nil.
  Error if arg is not nil and not a cons cell.  See also `cdr-safe'.
  
  See Info node `(elisp)Cons Cells' for a discussion of related basic