tabular: fix insertion of separator before 'cont

Use 'cont before a 'cont cell instead of adding a separator.

scribble-doc/scribblings/scribble/base.scrbl

@@ -265,7 +265,9 @@ If @racket[sep] is not @racket[#f], it is inserted as a new column
 between every column in the table; note that any
 @racket[table-columns] or @racket[table-cells] property in
 @racket[style] must take the added columns into account. Otherwise,
-the default style places no space between table columns.
+the default style places no space between table columns. When @racket[sep]
+would be placed before a @racket['cont], a @racket['cont] is inserted,
+instead.
 
 The @racket[column-properties], @racket[row-properties], and
 @racket[cell-properties] arguments specify @tech{style properties} for
@@ -324,7 +326,9 @@ properties will be used from the merger into @racket[table-cells].}
 
 @history[#:changed "1.1" @elem{Added the @racket[#:column-properties],
                                @racket[#:row-properties],
-                               and @racket[#:cell-properties] arguments.}]
+                               and @racket[#:cell-properties] arguments.}
+         #:changed "1.12" @elem{Changed @racket[sep] insertion before a
+                                @racket['cont].}]
 
 Examples:
 @codeblock[#:keep-lang-line? #f]|{

scribble-lib/info.rkt

@@ -24,4 +24,4 @@
 
 (define pkg-authors '(mflatt eli))
 
-(define version "1.11")
+(define version "1.12")

scribble-lib/scribble/base.rkt

@@ -554,10 +554,21 @@
                         [else (make-paragraph plain cell)]))
                      (define l (map cvt row))
                      (if sep
-                         (add-between l (cvt sep))
+                         (add-between/cont l (cvt sep))
                          l))
                    cells)))
 
+;; Like `add-between`, but change `sep` to 'cont when
+;; adding before a 'cont:
+(define (add-between/cont l sep)
+  (cond
+   [(null? l) null]
+   [(null? (cdr l)) l]
+   [else
+    (list* (car l)
+           (if (eq? 'cont (cadr l)) 'cont sep)
+           (add-between/cont (cdr l) sep))]))
+
 ;; ----------------------------------------
 
 (provide/contract

scribble-test/tests/scribble/docs/table.scrbl

@@ -18,3 +18,7 @@
           #:sep "-"
           (list (list "A" "B" "C" "D")
                 (list "apple" "banana" "coconut" "donut")))
+
+@(tabular #:sep "-"
+          (list (list "A" 'cont "C" 'cont 'cont)
+                (list "apple" "banana" "coconut" "donut" "eclair")))

scribble-test/tests/scribble/docs/table.txt

@@ -7,3 +7,6 @@ a    -b     -c      -d
 
     A-  B   -C      -D    
 apple-banana-coconut-donut
+
+A           -C                   
+apple-banana-coconut-donut-eclair