openssl: Fix (harmless) memory leaks at exit.

openssl: Fix (harmless) memory leaks at exit.

Without this, valgrind --leak-check=full --show-leak-kinds=all
complains about four memory blocks reachable at exit, see below.

The first leak is fixed by the new call to ERR_remove_thread_state(),
which frees the error queue of the current thread. To squash the
other three, the call to EVP_cleanup() is needed to remove all of
openssl's internal ciphers and digests.

To make this work on both openssl-1.0 and for openssl-1.1, we need
to add additional header checks for configure.

---
==2818== 12 bytes in 1 blocks are still reachable in loss record 1 of 4
==2818==    at 0x40355EE: malloc (vg_replace_malloc.c:309)
==2818==    by 0x41B887C: CRYPTO_malloc (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x42459B7: lh_insert (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4248542: int_thread_set_item (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4249920: ERR_get_state (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x424A255: ERR_put_error (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4222EF6: RSA_padding_check_PKCS1_OAEP_mgf1 (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x422306A: RSA_padding_check_PKCS1_OAEP (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x421F921: RSA_eay_private_decrypt (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x804F2E9: apc_priv_decrypt (openssl.c:206)
==2818==    by 0x804DB59: client_post_select (client_common.c:321)
==2818==    by 0x804CC57: call_post_select (sched.c:80)
==2818==    by 0x804CC57: sched_post_select (sched.c:106)
==2818==    by 0x804CC57: schedule (sched.c:159)
==2818==
==2818== 64 bytes in 1 blocks are still reachable in loss record 2 of 4
==2818==    at 0x40355EE: malloc (vg_replace_malloc.c:309)
==2818==    by 0x41B887C: CRYPTO_malloc (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4245643: lh_new (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x424811F: int_thread_get (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4248511: int_thread_set_item (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4249920: ERR_get_state (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x424A255: ERR_put_error (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4222EF6: RSA_padding_check_PKCS1_OAEP_mgf1 (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x422306A: RSA_padding_check_PKCS1_OAEP (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x421F921: RSA_eay_private_decrypt (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x804F2E9: apc_priv_decrypt (openssl.c:206)
==2818==    by 0x804DB59: client_post_select (client_common.c:321)
==2818==
==2818== 96 bytes in 1 blocks are still reachable in loss record 3 of 4
==2818==    at 0x40355EE: malloc (vg_replace_malloc.c:309)
==2818==    by 0x41B887C: CRYPTO_malloc (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4245628: lh_new (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x424811F: int_thread_get (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4248511: int_thread_set_item (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4249920: ERR_get_state (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x424A255: ERR_put_error (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4222EF6: RSA_padding_check_PKCS1_OAEP_mgf1 (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x422306A: RSA_padding_check_PKCS1_OAEP (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x421F921: RSA_eay_private_decrypt (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x804F2E9: apc_priv_decrypt (openssl.c:206)
==2818==    by 0x804DB59: client_post_select (client_common.c:321)
==2818==
==2818== 400 bytes in 1 blocks are still reachable in loss record 4 of 4
==2818==    at 0x40355EE: malloc (vg_replace_malloc.c:309)
==2818==    by 0x41B887C: CRYPTO_malloc (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x424988C: ERR_get_state (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x424A255: ERR_put_error (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x4222EF6: RSA_padding_check_PKCS1_OAEP_mgf1 (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x422306A: RSA_padding_check_PKCS1_OAEP (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x421F921: RSA_eay_private_decrypt (in /usr/local/lib/libcrypto.so.1.0.0)
==2818==    by 0x804F2E9: apc_priv_decrypt (openssl.c:206)
==2818==    by 0x804DB59: client_post_select (client_common.c:321)
==2818==    by 0x804CC57: call_post_select (sched.c:80)
==2818==    by 0x804CC57: sched_post_select (sched.c:106)
==2818==    by 0x804CC57: schedule (sched.c:159)
==2818==    by 0x804AB2D: main (client.c:656)