The patch adds DYNAMIC_ARRAY all_status_vars, which is now the
sole source of status information for SHOW STATUS.  Status
variables can be added to and removed from the array dynamically.
SHOW STATUS command uses this array instead of static array
from mysqld.cc
Compatibility with the old, global list of status variables is
preserved in init_server_components(), where this global list is
simply appended to all_status_vars.


include/plugin.h:
  WL#2935 - SHOW STATUS support in plugins
plugin/fulltext/plugin_example.c:
  WL#2935 - SHOW STATUS support in plugins
  example
sql/ha_innodb.cc:
  s/struct show_var_st/SHOW_VAR/
sql/ha_innodb.h:
  s/struct show_var_st/SHOW_VAR/
sql/mysql_priv.h:
  WL#2935 - SHOW STATUS support in plugins
  add_status_vars(), remove_status_vars()
sql/mysqld.cc:
  bug: plugin_free must be called even with --skip-grants
  add_status_vars()/free_status_vars(), remove unused SHOW_xxx_CONST
  s/struct show_var_st/SHOW_VAR/
sql/set_var.cc:
  s/struct show_var_st/SHOW_VAR/
sql/sql_parse.cc:
  s/struct show_var_st/SHOW_VAR/
sql/sql_plugin.cc:
  WL#2935 - SHOW STATUS support in plugins
sql/sql_plugin.h:
  WL#2935 - SHOW STATUS support in plugins
sql/sql_show.cc:
  WL#2935 - SHOW STATUS support in plugins
  DYNAMIC_ARRAY all_status_vars, add_status_vars(), remove_status_vars()
  s/struct show_var_st/SHOW_VAR/
sql/structs.h:
  WL#2935 - SHOW STATUS support in plugins
  SHOW STATUS definitions moved to include/plugin.h and sql_plugin.h
  s/struct show_var_st/SHOW_VAR/