iteration risk note

> instead of loading the whole result into memory at once
is not the full truth.

There is a certain risk of processes getting killed due to memory allocation with large iteration. This is caused by result buffering of the client not being visible to PHP and thus not from 'within' the process.

It is not certain that this occurs with all database clients but seems rather likely to at this point.

This is only a proposal for discussion as I am not certain how to best add the information or if to add it at all (was it obvious before?). Personally I got confused by the existing description and didn't notice the memory implication until further investigation using `top` reported the process to run at 3+GB memory while PHP reported 400M real peak usage.
Rebase to master
Revert tab changes
Revert docblock
Fix wrong logic
Add method to interface
Fix docblock
Remove useless exception
Fix tests
fallback to persister count
Fix test
Fix CS
Functional test
Add test
Fix bug with hydrators
CS fix
makes doctrine less dependent upon the symfony yamp component
Add SECURITY.md and a chapter on security assumptions in Doctrine ORM.
Merge branch 'master' of github.com:doctrine/doctrine2
allow passing EntityManagerInterface when creating a HelperSet