Bug#26030 (Parsing fails for stored routine w/multi-statement execution

enabled)

Before this fix, the lexer and parser would treat the ';' character as a
different token (either ';' or END_OF_INPUT), based on convoluted logic,
which failed in simple cases where a stored procedure is implemented as a
single statement, and used in a multi query.

With this fix:
- the character ';' is always parsed as a ';' token in the lexer,
- parsing multi queries is implemented in the parser, in the 'query:' rules,
- the value of thd->client_capabilities, which is the capabilities
  negotiated between the client and the server during bootstrap,
  is immutable and not arbitrarily modified during parsing (which was the
  root cause of the bug)

mysql-test/t/parser.test

@@ -0,0 +1,59 @@
+#
+# This file contains tests covering the parser
+#
+
+#=============================================================================
+# LEXICAL PARSER (lex)
+#=============================================================================
+
+#
+# Maintainer: these tests are for the lexical parser, so every character,
+# even whitespace or comments, is significant here.
+#
+
+#
+# Bug#26030 (Parsing fails for stored routine w/multi-statement execution
+# enabled)
+#
+
+--disable_warnings
+DROP PROCEDURE IF EXISTS p26030;
+--enable_warnings
+
+delimiter $$;
+
+select "non terminated"$$
+select "terminated";$$
+select "non terminated, space"      $$
+select "terminated, space";      $$
+select "non terminated, comment" /* comment */$$
+select "terminated, comment"; /* comment */$$
+
+# Multi queries can not be used in --ps-protocol test mode
+--disable_ps_protocol
+
+select "stmt 1";select "stmt 2 non terminated"$$
+select "stmt 1";select "stmt 2 terminated";$$
+select "stmt 1";select "stmt 2 non terminated, space"      $$
+select "stmt 1";select "stmt 2 terminated, space";      $$
+select "stmt 1";select "stmt 2 non terminated, comment" /* comment */$$
+select "stmt 1";select "stmt 2 terminated, comment"; /* comment */$$
+
+select "stmt 1";             select "space, stmt 2"$$
+select "stmt 1";/* comment */select "comment, stmt 2"$$
+
+DROP PROCEDURE IF EXISTS p26030; CREATE PROCEDURE p26030() BEGIN SELECT 1; END; CALL p26030()
+$$
+
+DROP PROCEDURE IF EXISTS p26030; CREATE PROCEDURE p26030() SELECT 1; CALL p26030()
+$$
+
+--enable_ps_protocol
+
+delimiter ;$$
+DROP PROCEDURE p26030;
+
+#============================================================================r
+# SYNTACTIC PARSER (bison)
+#=============================================================================
+