Memory usage too high during archiving process

[matt]

The memory usage seems too high during the archiving process.

There is need to

1. profile the memory using Xdebug
2. find potential memory leaks during archiving
3. write documentation on how to optimize memory usage so people don't hit php memory limit too often (archive in multiple steps?)

[matt]

Fixed a memory leak problem, and introduced the dataTable truncation after N rows. Seems to work really well now.

[matt]

(In [1133]) - test server upgrade refs #3

[matt]

(In [1688]) Refs #3 test post commit