mysqldump --tab still dumped triggers to stdout rather than to
individual tables.

We now append triggers to the .sql file for the corresponding
table.

--events and --routines correspond to a database rather than a
table and will still go to stdout with --tab unless redirected
with --result-file (-r).

client/mysqldump.c:
  Extend open_sql_file_for_table() so we can open-append.
  Change dump_triggers_for_table() so it will append its
  output to the table's .sql-file when --tab is used.
mysql-test/r/mysqldump.result:
  Show that when using --tab, triggers now end up in the .sql
  file with the corresponding table (after that table), while
  --routines and --events go to stdout or --result-file.
mysql-test/t/mysqldump.test:
  Show that when using --tab, triggers now end up in the .sql
  file with the corresponding table (after that table), while
  --routines and --events go to stdout or --result-file.