SERVER-13715 plan subqueries on construction of a SubplanRunner

This enforces the error behavior expected by aggregation.
(cherry picked from commit 20263ce4e9c345a2d3748ef2071f6dc860a092f1)
SERVER-13715 fix use of auto_ptr after release in subplan runner
(cherry picked from commit 193aba81f1c9c9c0c0a7e9ba857e7538dc6b6ed0)