[Rd] libz>=1.2.1 requirement - necessary?

[Simon Urbanek]

I the course of cleaning up the build for OS X I wondered why R 
requires zlib 1.2.1+. Is there any specific reason for that? OS X comes 
with zlib 1.1.4, so I wonder if using the system library has any 
drawbacks... (it worked for me, but..). I found nothing in the 
archives, but maybe someone remembers?

Cheers,
Simon