Also make InnoDB thinks that /*/ only starts a comment. (Bug #53644).

This fixes the bugs in the InnoDB Plugin.

ha_innodb.h: Use trx_query_string() instead of trx_query() when
available (MySQL 5.1.42 or later).

innobase_get_stmt(): New function, to retrieve the currently running
SQL statement.

struct trx_struct: Remove mysql_query_str. Use innobase_get_stmt() instead.

dict_strip_comments(): Add and observe the parameter sql_length. Treat
/*/ as the start of a comment.

dict_create_foreign_constraints(), row_table_add_foreign_constraints():
Add the parameter sql_length.