Add new line.
Add itersource.
Add itersource test.
The itersource iterables key is a tuple only if there is more than one itersource iterable field.
Remove spurious line.
Flush out the itersource test.
Build the itersource iterables from the ancestor value lookup.
Add back the graph merge lines.
Merge branch 'itersource' into join_itersource

Conflicts:
	nipype/pipeline/utils.py
Fix _iterable_nodes merge.
Support join on a node with an itersource.
Merge branch 'join_itersource'
Add iterables synchronize.
Merge branch 'join_itersource_synchronize'
Clarify comment.
Refactor iterable standardization to account for the itersource alternate format.
Test the alternate itersource iterables format.
Add the itersource field.
Merge branch 'join_itersource_synchronize'