Fixed memory leak caused by mempool related to request context.
Fixed memory leak caused by mempool related to request context.

The previous attempt of fixing this in e5a65b58101f hasn't been really
successful, because the actual memory leak was caused not by the request
parse context itself, but its memory pool.

nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit,nginx/unit