in r2276.  Now the following symbols will be exported when InnoDB is built
as a dynamic plugin:

* the virtual method pointer table of class ha_innodb
* the three variables that MySQL will reference when linking at runtime:

	_mysql_plugin_declarations_
	_mysql_plugin_interface_version_
	_mysql_sizeof_struct_st_plugin_

Furthermore, the following symbols are weak globals, to allow us to access
the built-in InnoDB in the mysqld executable, in case it contains a statically
linked InnoDB:

	builtin_innobase_plugin
	innodb_hton_ptr