finalized basic garbage collection

Summary:
after a lot of work I got to the bottom of the memory leak

Fixes T7476

Test Plan: none

Reviewers: ankur

Maniphest Tasks: T7476

Differential Revision: http://grizzly.memsql.com/D3786
2013-09-26 Version 2.3.3

    * Implemented garbage collection for very old pending analytical rows