Various doc fixes.

Make all mention of digest algorithm use "any supported algorithm"

RT2071, some new manpages from Victor B. Wagner <vitus@cryptocom.ru>:
    X509_LOOKUP_hash_dir.pod
    X509_check_ca.pod
    X509_check_issued.pod

RT 1600:
    Remove references to non-existant objects(3)
    Add RETURN VALUES to BIO_do_accept page.

RT1818:
    RSA_sign Can return values other than 0 on failure.

RT3634:
    Fix AES CBC aliases (Steffen Nurpmeso <sdaoden@yandex.com>)

RT3678:
    Some clarifications to BIO_new_pair
    (Devchandra L Meetei <dlmeetei@gmail.com>)

RT3787:
    Fix some EVP_ function return values
    (Laetitia Baudoin <lbaudoin@google.com>)

Reviewed-by: Tim Hudson <tjh@openssl.org>