RT1771: Add string.h include.

Reviewed-by: Dr. Stephen Henson <steve@openssl.org>
(cherry picked from commit 8842987e5a76535597b9795b0408565baabf18d1)
RT1832: Fix PKCS7_verify return value

The function returns 0 or 1, only.

Reviewed-by: Dr. Stephen Henson <steve@openssl.org>
(cherry picked from commit b0e659cfaca9ff4a481cc63b7f6b6e97303ad8fe)