libssh2: revision bump to fix CVE-2016-0787

- adds patch copied from Debian to address CVE
- fixes zlib detection
- changes http to https links
- updates maintainer's mail address

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

libs/libssh2/patches/0004-CVE-2016-0787.patch

@@ -0,0 +1,22 @@
+Description: CVE-2016-0787: Truncated Difffie-Hellman secret length
+ Convert bytes to bits in diffie_hellman_sha1. Otherwise we get far too
+ small numbers.
+Origin: backport, http://www.libssh2.org/CVE-2016-0787.patch
+Forwarded: not-needed
+Author: Daniel Stenberg <daniel@haxx.se>
+Reviewed-by: Salvatore Bonaccorso <carnil@debian.org>
+Last-Update: 2016-02-18
+Applied-Upstream: 1.7.0
+---
+
+--- a/src/kex.c
++++ b/src/kex.c
+@@ -103,7 +103,7 @@ static int diffie_hellman_sha1(LIBSSH2_S
+         memset(&exchange_state->req_state, 0, sizeof(packet_require_state_t));
+ 
+         /* Generate x and e */
+-        _libssh2_bn_rand(exchange_state->x, group_order, 0, -1);
++        _libssh2_bn_rand(exchange_state->x, group_order * 8 - 1, 0, -1);
+         _libssh2_bn_mod_exp(exchange_state->e, g, exchange_state->x, p,
+                             exchange_state->ctx);
+