Add Slave_skipped_errors to global status

This counts the number of times a replication event is ignored
due to slave_skip_errors.

mysql-test/suite/engines/funcs/t/rpl_variables.test

@@ -15,6 +15,7 @@ show variables like 'slave_load_tmpdir';
 # We just set some arbitrary values in variables-master.opt so we can test
 # that a list of values works correctly
 show variables like 'slave_skip_errors';
+show global status like 'slave_skipped_errors';
 
 # Cleanup
 set global slave_net_timeout=@my_slave_net_timeout;

sql/log_event.cc

@@ -440,8 +440,12 @@ inline int ignored_error_code(int err_code)
     break;
   }
 #endif
-  return ((err_code == ER_SLAVE_IGNORED_TABLE) ||
-          (use_slave_mask && bitmap_is_set(&slave_error_mask, err_code)));
+  if (use_slave_mask && bitmap_is_set(&slave_error_mask, err_code))
+  {
+    statistic_increment(slave_skipped_errors, LOCK_status);
+    return true;
+  }
+  return err_code == ER_SLAVE_IGNORED_TABLE;
 }
 
 /*

sql/mysqld.cc

@@ -516,6 +516,7 @@ ulong binlog_stmt_cache_use= 0, binlog_stmt_cache_disk_use= 0;
 ulong max_connections, max_connect_errors;
 ulong extra_max_connections;
 ulong slave_retried_transactions;
+ulonglong slave_skipped_errors;
 ulong feature_files_opened_with_delayed_keys;
 ulonglong denied_connections;
 my_decimal decimal_zero;
@@ -7921,6 +7922,7 @@ SHOW_VAR status_vars[]= {
   {"Slave_received_heartbeats",(char*) &show_slave_received_heartbeats, SHOW_SIMPLE_FUNC},
   {"Slave_retried_transactions",(char*)&slave_retried_transactions, SHOW_LONG},
   {"Slave_running",            (char*) &show_slave_running,     SHOW_SIMPLE_FUNC},
+  {"Slave_skipped_errors",     (char*) &slave_skipped_errors, SHOW_LONGLONG},
 #endif
   {"Slow_launch_threads",      (char*) &slow_launch_threads,    SHOW_LONG},
   {"Slow_queries",             (char*) offsetof(STATUS_VAR, long_query_count), SHOW_LONG_STATUS},

sql/slave.h

@@ -130,6 +130,7 @@ extern my_bool opt_log_slave_updates;
 extern char *opt_slave_skip_errors;
 extern my_bool opt_replicate_annotate_row_events;
 extern ulonglong relay_log_space_limit;
+extern ulonglong slave_skipped_errors;
 
 /*
   3 possible values for Master_info::slave_running and