by moving yet another relevant flag to it from struct LEX.


mysql-test/r/ps.result:
  Update result.
mysql-test/r/ps_1general.result:
  Update result.
mysql-test/t/ps.test:
  New error code.
mysql-test/t/ps_1general.test:
  New error code.
sql/sql_lex.cc:
  Move stmt_prepare_mode to Lex_input_stream.
sql/sql_lex.h:
  Move stmt_prepare_mode to class Lex_input_stream
sql/sql_prepare.cc:
  Move stmt_prepare_mode to Lex_input_stream
sql/sql_yacc.yy:
  Remove dead code.