Fixed bug #29294.

The `SELECT 'r' INTO OUTFILE ... FIELDS ENCLOSED BY 'r' ' statement
encoded the 'r' string to a 4 byte string of value x'725c7272'
(sequence of 4 characters: r\rr).
The LOAD DATA statement decoded this string to a 1 byte string of
value x'0d' (ASCII Carriage Return character) instead of the original
'r' character.
The same error also happened with the FIELDS ENCLOSED BY clause
followed by special characters: 'n', 't', 'r', 'b', '0', 'Z' and 'N'.

NOTE 1: This is a result of the undocumented feature: the LOAD DATA INFILE
recognises 2-byte input sequences like \n, \t, \r and \Z in addition
to documented 2-byte sequences: \0 and \N. This feature should be
documented (here backspace character is a default ESCAPED BY character,
in the real-life example it may be any ESCAPED BY character).

NOTE 2, changed behaviour:
Now the `SELECT INTO OUTFILE' statement with the `FIELDS ENCLOSED BY'
clause followed by one of: 'n', 't', 'r', 'b', '0', 'Z' or 'N' characters
encodes this special character itself by doubling it ('r' --> 'rr'),
not by prepending it with an escape character.

mysql-test/r/loaddata.result

@@ -1,4 +1,4 @@
-drop table if exists t1;
+drop table if exists t1,t2;
 create table t1 (a date, b date, c date not null, d date);
 load data infile '../../std_data/loaddata1.dat' into table t1 fields terminated by ',';
 Warnings:
@@ -85,3 +85,66 @@ field1	field2
 a"b	cd"ef
 a"b	c"d"e
 drop table t1;
+CREATE TABLE t1 (
+id INT AUTO_INCREMENT PRIMARY KEY,
+c1 VARCHAR(255)
+);
+CREATE TABLE t2 (
+id INT,
+c2 VARCHAR(255)
+);
+INSERT INTO t1 (c1) VALUES
+('r'),   ('rr'),   ('rrr'),   ('rrrr'),
+('.r'),  ('.rr'),  ('.rrr'),  ('.rrrr'),
+('r.'),  ('rr.'),  ('rrr.'),  ('rrrr.'),
+('.r.'), ('.rr.'), ('.rrr.'), ('.rrrr.'),
+('\r'),  ('\\rr'), ('\\\rr'), ('\\\\rr');
+SELECT * FROM t1;
+id	c1
+1	r
+2	rr
+3	rrr
+4	rrrr
+5	.r
+6	.rr
+7	.rrr
+8	.rrrr
+9	r.
+10	rr.
+11	rrr.
+12	rrrr.
+13	.r.
+14	.rr.
+15	.rrr.
+16	.rrrr.
+17	
+18	\rr
+19	\
+r
+20	\\rr
+SELECT * INTO OUTFILE 'MYSQL_TEST_DIR/var/tmp/t1' FIELDS ENCLOSED BY 'r' FROM t1;
+r1r	rrrr
+r2r	rrrrrr
+r3r	rrrrrrrr
+r4r	rrrrrrrrrr
+r5r	r.rrr
+r6r	r.rrrrr
+r7r	r.rrrrrrr
+r8r	r.rrrrrrrrr
+r9r	rrr.r
+r10r	rrrrr.r
+r11r	rrrrrrr.r
+r12r	rrrrrrrrr.r
+r13r	r.rr.r
+r14r	r.rrrr.r
+r15r	r.rrrrrr.r
+r16r	r.rrrrrrrr.r
+r17r	r
+r
+r18r	r\\rrrrr
+r19r	r\\
+rrr
+r20r	r\\\\rrrrr
+LOAD DATA INFILE 'MYSQL_TEST_DIR/var/tmp/t1' INTO TABLE t2 FIELDS ENCLOSED BY 'r';
+SELECT t1.id, c1, c2 FROM t1 LEFT  JOIN t2 ON t1.id=t2.id WHERE c1 != c2;
+id	c1	c2