[Rd] mem.limits deprecated

[Jeroen Ooms]

After upgrading my servers to 2.14, log files were filled warnings
that 'mem.limits' has been deprecated and to use gc instead. After
reading the NEWS for R 2.14.0 and PR#14795 I learned that it is
actually deprecated without replacement.

Hereby I just want to voice that this function was actually in use by
at least several users. Among other things, it is a useful to limit
per-session memory on a shared resource. I am not sure what the
assumption that 'these limits are nowadays almost never used' was
based on, but I would disagree.

Obviously this is message is late, the decision has been made and we
were not paying attention when we should have. However if there is
possibly anything that can be done to rescue some of this
functionality that would be greatly appreciated. E.g. by keeping some
of the support in the memory allocator and moving the R code into a
package or so.

Thank you