On access path code block support:
{pre, post} are not allowed to contain 'tuple_iter'
in order to distinguish them. If such is neccessary,
write a custom function and call it in the access path.
If uses cases for such code block access paths
are brought up, we will redesign.
Merge branch 'master' of https://github.com/mfragkoulis/PiCO_QL
	Forgot to pull before making local changes.