Error: C stack usage 9521780 is too close to the limit

[vspinu]

## on R version 3.4.0 Patched (2017-05-25 [r72739)
> dyears(1) >  years(3)
Error: C stack usage  9521780 is too close to the limit

## on R version 3.3.3 (2017-03-06)
> dyears(1) > years(1)
Error: evaluation nested too deeply: infinite recursion / options(expressions=)?

> years(1) > dyears(1) ## works as expected, throws