adjust ascii-box => unicode-box algorithm so that

it only looks left and right at hyphens and only
up and down at pipes, etc. This better handles the
case where you have something like this:

  +--------------+
  | (<= a-x b-y) |
  +--------------+

Before this commit, it would have adjusted the hypens
inside the identifiers

collects/framework/private/keymap.rkt

@@ -1499,14 +1499,15 @@
       (unless (hash-ref visited pos #f)
         (hash-set! visited pos #t)
         (define-values (x y) (pos->xy t pos))
+        (define c (send t get-character pos))
         (define up (xy->pos t x (- y 1)))
         (define dn (xy->pos t x (+ y 1)))
         (define lt (xy->pos t (- x 1) y))
         (define rt (xy->pos t (+ x 1) y))
-        (define i-up? (i? t up))
-        (define i-dn? (i? t dn))
-        (define i-lt? (i? t lt))
-        (define i-rt? (i? t rt))
+        (define i-up? (and (i? t up) (member c up-chars)))
+        (define i-dn? (and (i? t dn) (member c dn-chars)))
+        (define i-lt? (and (i? t lt) (member c lt-chars)))
+        (define i-rt? (and (i? t rt) (member c rt-chars)))
         (cond
           [(and i-up? i-dn? i-lt? i-rt?) (set t pos "╬")]
           [(and i-dn? i-lt? i-rt?)       (set t pos "╦")]
@@ -1539,12 +1540,37 @@
   (define start (send text paragraph-start-position para))
   (values (- pos start) para))
 
-(define adjustable-chars
+(define up-chars
   '(#\╬ 
-    #\╩ #\╦ #\╣ #\╠
-    #\╝ #\╗ #\╔ #\╚
-    #\═ #\║
-    #\+ #\- #\|))
+    #\╩ #\╣ #\╠
+    #\╝ #\╚
+    #\║
+    #\+ #\|))
+
+(define dn-chars
+  '(#\╬ 
+    #\╦ #\╣ #\╠
+    #\╗ #\╔
+    #\║
+    #\+ #\|))
+
+(define lt-chars
+  '(#\╬ 
+    #\╩ #\╦ #\╣
+    #\╝ #\╗ 
+    #\═ 
+    #\+ #\-))
+
+(define rt-chars
+  '(#\╬ 
+    #\╩ #\╦ #\╠
+    #\╔ #\╚
+    #\═
+    #\+ #\-))
+
+(define adjustable-chars
+  (remove-duplicates
+   (append up-chars dn-chars lt-chars rt-chars)))
 
 
 (define (xy->pos text x y)

collects/tests/framework/keys.rkt

@@ -290,6 +290,14 @@
                          (string-append "╔═╗\n"
                                         "║ ║\n"
                                         "╚═╝\n"))
+     (ascii-art-box-spec (string-append "+---+\n"
+                                        "| - |\n"
+                                        "|+ ||\n"
+                                        "+---+\n")
+                         (string-append "╔═══╗\n"
+                                        "║ - ║\n"
+                                        "║+ |║\n"
+                                        "╚═══╝\n"))
      (ascii-art-box-spec (string-append "+-+-+\n"
                                         "| | |\n"
                                         "+-+-+\n"