Closes #5528 - setDF.
GForce is optimised to work with j-expressions with .N. FR #5760
Using .I in j will name the column as "I", similar to .N's usage. FR #5290.
Merge branch 'refs/heads/5760'

Conflicts:
	pkg/NEWS
	pkg/inst/tests/tests.Rraw
Merge branch 'refs/heads/5290'

Conflicts:
	pkg/NEWS