RT2518: fix pod2man errors

pod2man now complains when item tags are not sequential.
Also complains about missing =back and other tags.
Silence the warnings; most were already done.

Reviewed-by: Tim Hudson <tjh@openssl.org>
(cherry picked from commit fe7573042fa7f406fedb78d959659b39a7a1dcfb)
RT3301: Discard too-long heartbeat requests

Reviewed-by: Tim Hudson <tjh@openssl.org>
(cherry picked from commit af4c6e348e4bad6303e7d214cdcf2536487aabe4)
RT468: SSL_CTX_sess_set_cache_size wrong

The documentation is wrong about what happens when the
session cache fills up.

Reviewed-by: Tim Hudson <tjh@openssl.org>
(cherry picked from commit e9edfc419674f20b482a9beff9c246519f9c503e)