What to do about the reserve functions

[AaronKutch]

I must have looked over the Vec::reserve documentation a dozen times, and somehow I never noticed that it reserves at least self.len() + additional and not self.capacity() + additional, meaning that self.reserve(self.capacity()) can do nothing instead of doubling the capacity. I only now found about this in another project where it caused an unexpected infinite loop. The previous versions of triple_arena happened to be ultimately based on length and never encountered the problem, and in the current version NonZeroInxVec uses the formulation I always assumed was the case. Should I change the behavior of all the reserve functions?