copy a comment placed in other files; req from miod
Add a comment documenting where libssl depends upon the current (objectionable)
behaviour of this code, to prevent people from blindly changing it.
BUF_MEM_grow_clean() takes a size_t as the size argument. Remove false comments
mentioning it's an int, bogus (int) casts and bounds checks against INT_MAX
(BUF_MEM_grow_clean has its own integer bounds checks).

ok deraadt@