Use single constant-time memory comparison implementation
* src/const-time.c (ct_not_memequal): Use original 'buf_eq_const' implementation here. (ct_memequal): New. * cipher/bufhelp.h (buf_eq_const): Call to 'ct_memequal'.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>