Backporting Bug#32391 Character sets: crash with --character-set-server

from mysql-trunk-bugfixing (5.6.1-m5) from mysql-5.5-bugfixing (5.5.6-m3).

mysql-test/r/ctype_utf16_def.result

+SHOW VARIABLES LIKE 'collation_server';
+Variable_name	Value
+collation_server	utf16_general_ci
+SHOW VARIABLES LIKE 'character_set_server';
+Variable_name	Value
+character_set_server	utf16
+SHOW VARIABLES LIKE 'ft_stopword_file';
+Variable_name	Value
+ft_stopword_file	(built-in)

mysql-test/t/ctype_utf16_def-master.opt

+--character-set-server=utf16,latin1

mysql-test/t/ctype_utf16_def.test

+--source include/have_utf16.inc
+
+#
+# Bug #32391  	Character sets: crash with --character-set-server
+# 
+SHOW VARIABLES LIKE 'collation_server';
+SHOW VARIABLES LIKE 'character_set_server';
+SHOW VARIABLES LIKE 'ft_stopword_file';

storage/myisam/ft_stopwords.c

@@ -18,6 +18,10 @@
 #include "ftdefs.h"
 #include "my_handler.h"
 
+
+static CHARSET_INFO *ft_stopword_cs= NULL;
+
+
 typedef struct st_ft_stopwords
 {
   const char * pos;
@@ -29,7 +33,7 @@ static TREE *stopwords3=NULL;
 static int FT_STOPWORD_cmp(void* cmp_arg __attribute__((unused)),
 			   FT_STOPWORD *w1, FT_STOPWORD *w2)
 {
-  return ha_compare_text(default_charset_info,
+  return ha_compare_text(ft_stopword_cs,
 			 (uchar *)w1->pos,w1->len,
 			 (uchar *)w2->pos,w2->len,0,0);
 }
@@ -59,6 +63,14 @@ int ft_init_stopwords()
               0,
               (ft_stopword_file ? (tree_element_free)&FT_STOPWORD_free : 0),
               NULL);
+    /*
+      Stopword engine currently does not support tricky
+      character sets UCS2, UTF16, UTF32.
+      Use latin1 to compare stopwords in case of these character sets.
+      It's also fine to use latin1 with the built-in stopwords.
+    */
+    ft_stopword_cs= default_charset_info->mbminlen == 1 ?
+                    default_charset_info : &my_charset_latin1;
   }
 
   if (ft_stopword_file)
@@ -80,7 +92,7 @@ int ft_init_stopwords()
       goto err0;
     len=my_read(fd, buffer, len, MYF(MY_WME));
     end=start+len;
-    while (ft_simple_get_word(default_charset_info, &start, end, &w, TRUE))
+    while (ft_simple_get_word(ft_stopword_cs, &start, end, &w, TRUE))
     {
       if (ft_add_stopword(my_strndup((char*) w.pos, w.len, MYF(0))))
         goto err1;