bug#6902: 23.2; indent-line-to possible devide by zero error bug

[Arik Mitschang]

In indent.el the indent-line-to function has a comparison that devides
the current column count by tab-width, whose value is an integerp and
allowed to be zero (and in my experience is often 0). I noticed the
issue in specific with org mode which utilizes this function for a lot
of interesting tasks.

I can provide the following patch which makes a check to avoid an
arithmetic error:

=== modified file 'lisp/indent.el'
--- lisp/indent.el      2010-05-19 03:06:48 +0000
+++ lisp/indent.el      2010-08-24 15:20:39 +0000
@@ -177,7 +177,9 @@
   (back-to-indentation)
   (let ((cur-col (current-column)))
     (cond ((< cur-col column)
-          (if (>= (- column (* (/ cur-col tab-width) tab-width)) tab-width)
+          (if (and (> tab-width 0)
+                   (>= (- column (* (/ cur-col tab-width) tab-width)) 
+                       tab-width))
               (delete-region (point)
                              (progn (skip-chars-backward " ") (point))))
           (indent-to column))

Thanks,
~Arik