Also, fixes the memory allocation bug - misuse of mem_ensure that caused to allocate 72 bytes of memory to carry 16 bytes of data for instance. Fixes golang/go#11842. Change-Id: I21798be2ec7adfb68cc2897bb46a924f05f3478c Reviewed-on: https://go-review.googlesource.com/12577 Reviewed-by: David Crawshaw <crawshaw@golang.org>