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, 10 insertions, 0 deletions

diff --git a/sql/repl_failsafe.cc b/sql/repl_failsafe.cc
index d7e783f534f..582348608de 100644
--- a/sql/repl_failsafe.cc
+++ b/sql/repl_failsafe.cc
@@ -644,6 +644,16 @@ err:
 }
 #endif
 
+
+/**
+  Execute a SHOW SLAVE HOSTS statement.
+
+  @param thd Pointer to THD object for the client thread executing the
+  statement.
+
+  @retval FALSE success
+  @retval TRUE failure
+*/
 bool show_slave_hosts(THD* thd)
 {
   List<Item> field_list;