Bug#4521: unique key prefix interacts poorly with utf8.

Fix for binary collations for MyISAM and HEAP BTREE.
This patch also changes trailing spaces behaviour for
binary collations. Binary collations now have PAD 
characteristic too.

strings/ctype-mb.c

@@ -360,11 +360,62 @@ static int my_strnncoll_mb_bin(CHARSET_INFO * cs __attribute__((unused)),
   return cmp ? cmp : (int) ((t_is_prefix ? len : slen) - tlen);
 }
 
+
+/*
+  Compare two strings. 
+  
+  SYNOPSIS
+    my_strnncollsp_mb_bin()
+    cs			Chararacter set
+    s			String to compare
+    slen		Length of 's'
+    t			String to compare
+    tlen		Length of 't'
+
+  NOTE
+   This function is used for character strings with binary collations.
+   It ignores trailing spaces.
+
+  RETURN
+    A negative number if s < t
+    A positive number if s > t
+    0 if strings are equal
+*/
+
 static int my_strnncollsp_mb_bin(CHARSET_INFO * cs __attribute__((unused)),
-                                 const uchar *s, uint slen,
-                                 const uchar *t, uint tlen)
+                                 const uchar *a, uint a_length, 
+                                 const uchar *b, uint b_length)
 {
-  return my_strnncoll_mb_bin(cs,s,slen,t,tlen,0);
+  const uchar *end;
+  uint length;
+  
+  end= a + (length= min(a_length, b_length));
+  while (a < end)
+  {
+    if (*a++ != *b++)
+      return ((int) a[-1] - (int) b[-1]);
+  }
+  if (a_length != b_length)
+  {
+    int swap= 0;
+    /*
+      Check the next not space character of the longer key. If it's < ' ',
+      then it's smaller than the other key.
+    */
+    if (a_length < b_length)
+    {
+      /* put shorter key in s */
+      a_length= b_length;
+      a= b;
+      swap= -1;					/* swap sign of result */
+    }
+    for (end= a + a_length-length; a < end ; a++)
+    {
+      if (*a != ' ')
+	return ((int) *a - (int) ' ') ^ swap;
+    }
+  }
+  return 0;
 }