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.


sql/sql_class.h:
  Fixed bug #29294.
  The ESCAPE_CHARS macro constant is defined to enumerate
  symbolic names of espace-sequences like  '\n', '\t' etc.
  The select_export::is_ambiguous_field_sep field has been added
  to distinguish special values of the field_sep field from
  another values (see ESCAPE_CHARS).
sql/sql_class.cc:
  Fixed bug #29294.
  The select_export::send_data method has been modified to
  encode special values of the field_sep field by
  doubling of those values instead of prepending them with a
  value of the escape_char field.
  Example: The SELECT 'r' INTO OUTFILE FIELDS ENCLOSED BY 'r'
  now produces the 'rr' output string instead of x'5c72'
  (i.e. instead of sequence of 2 bytes: \ and r).
sql/sql_load.cc:
  Fixed bug #29294.
  Added commentary for the READ_INFO::unescape method.
mysql-test/t/loaddata.test:
  Updated test case for bug #29294.
mysql-test/r/loaddata.result:
  Updated test case for bug #29294.