BUG#41924: high-level replication functions are not commented

Adding comments to some of the high-level functions in replication.

sql/log_event.h:
  Fixed some mistakes in comments.
sql/repl_failsafe.cc:
  Added comment for show_slave_hosts()
sql/slave.cc:
  Added comment for show_master_info(), handle_slave_[sql|io](), and next_event()
sql/sql_binlog.cc:
  Added @param comment.
sql/sql_lex.h:
  Added comment for st_lex_master_info.
sql/sql_repl.cc:
  Added comments for functions executing a statement:
      PURGE BINARY LOGS
      START SLAVE
      STOP SLAVE
      RESET SLAVE
      CHANGE MASTER
      RESET MASTER
      SHOW BINLOG EVENTS
      SHOW MASTER STATUS
      SHOW BINARY LOGS

1 files changed, 9 insertions, 0 deletions

diff --git a/sql/sql_lex.h b/sql/sql_lex.h
index 26bd8d18750..ed6b9e7d8df 100644
--- a/sql/sql_lex.h
+++ b/sql/sql_lex.h
@@ -190,6 +190,15 @@ typedef struct st_lex_server_options
   char *server_name, *host, *db, *username, *password, *scheme, *socket, *owner;
 } LEX_SERVER_OPTIONS;
 
+
+/**
+  Structure to hold parameters for CHANGE MASTER or START/STOP SLAVE
+  or SHOW NEW MASTER.
+
+  Remark: this should not be confused with Master_info (and perhaps
+  would better be renamed to st_lex_replication_info).  Some fields,
+  e.g., delay, are saved in Relay_log_info, not in Master_info.
+*/
 typedef struct st_lex_master_info
 {
   char *host, *user, *password, *log_file_name;