Bug# 30946: mysqldump silently ignores --default-character-set

when used with --tab

1) New syntax: added CHARACTER SET clause to the
  SELECT ... INTO OUTFILE (to complement the same clause in
  LOAD DATA INFILE).
  mysqldump is updated to use this in --tab mode.

2) ESCAPED BY/ENCLOSED BY field parameters are documented as
   accepting CHAR argument, however SELECT .. INTO OUTFILE
   silently ignored rests of multisymbol arguments.
   For the symmetrical behavior with LOAD DATA INFILE the
   server has been modified to fail with the same error:

     ERROR 42000: Field separator argument is not what is
                  expected; check the manual

3) Current LOAD DATA INFILE recognizes field/line separators
   "as is" without converting from client charset to data
   file charset. So, it is supposed, that input file of
   LOAD DATA INFILE consists of data in one charset and
   separators in other charset. For the compatibility with
   that [buggy] behaviour SELECT INTO OUTFILE implementation
   has been saved "as is" too, but the new warning message
   has been added:

     Non-ASCII separator arguments are not fully supported

   This message warns on field/line separators that contain
   non-ASCII symbols.

sql/sql_string.h

@@ -40,6 +40,9 @@ uint32 well_formed_copy_nchars(CHARSET_INFO *to_cs,
 size_t my_copy_with_hex_escaping(CHARSET_INFO *cs,
                                  char *dst, size_t dstlen,
                                  const char *src, size_t srclen);
+uint convert_to_printable(char *to, size_t to_len,
+                          const char *from, size_t from_len,
+                          CHARSET_INFO *from_cs, size_t nbytes= 0);
 
 class String
 {
@@ -366,6 +369,19 @@ public:
   {
     return (s->alloced && Ptr >= s->Ptr && Ptr < s->Ptr + s->str_length);
   }
+  bool is_ascii() const
+  {
+    if (length() == 0)
+      return TRUE;
+    if (charset()->mbminlen > 1)
+      return FALSE;
+    for (const char *c= ptr(), *end= c + length(); c < end; c++)
+    {
+      if (!my_isascii(*c))
+        return FALSE;
+    }
+    return TRUE;
+  }
 };
 
 static inline bool check_if_only_end_space(CHARSET_INFO *cs, char *str,