Added support for replication for S3

MDEV-19964 S3 replication support

Added new configure options:
s3_slave_ignore_updates
"If the slave has shares same S3 storage as the master"

s3_replicate_alter_as_create_select
"When converting S3 table to local table, log all rows in binary log"

This allows on to configure slaves to have the S3 storage shared or
independent from the master.

Other thing:
Added new session variable '@@sql_if_exists' to force IF_EXIST to DDL's.

sql/sql_priv.h

@@ -146,7 +146,7 @@
 /** The following speeds up inserts to InnoDB tables by suppressing unique
    key checks in some cases */
 #define OPTION_RELAXED_UNIQUE_CHECKS    (1ULL << 27) // THD, user, binlog
-#define SELECT_NO_UNLOCK                (1ULL << 28) // SELECT, intern
+#define OPTION_IF_EXISTS                (1ULL << 28) // binlog
 #define OPTION_SCHEMA_TABLE             (1ULL << 29) // SELECT, intern
 /** Flag set if setup_tables already done */
 #define OPTION_SETUP_TABLES_DONE        (1ULL << 30) // intern
@@ -179,7 +179,7 @@
 #define OPTION_RPL_SKIP_PARALLEL        (1ULL << 38)
 #define OPTION_NO_QUERY_CACHE           (1ULL << 39) // SELECT, user
 #define OPTION_PROCEDURE_CLAUSE         (1ULL << 40) // Internal usage
-
+#define SELECT_NO_UNLOCK                (1ULL << 41) // SELECT, intern
 
 #define OPTION_LEX_FOUND_COMMENT        (1ULL << 0) //  intern, parser