Log Message:
libssh2: Update to 1.9.0

Changes:
- adds ECDSA keys and host key support when using OpenSSL
- adds ED25519 key and host key support when using OpenSSL 1.1.1
- adds OpenSSH style key file reading
- adds AES CTR mode support when using WinCNG
- adds PEM passphrase protected file support for Libgcrypt and WinCNG
- adds SHA256 hostkey fingerprint
- adds libssh2_agent_get_identity_path() and libssh2_agent_set_identity_path()
- adds explicit zeroing of sensitive data in memory
- adds additional bounds checks to network buffer reads
- adds the ability to use the server default permissions when creating sftp \ 
directories
- adds support for building with OpenSSL no engine flag
- adds support for building with LibreSSL
- increased sftp packet size to 256k
- fixed oversized packet handling in sftp
- fixed building with OpenSSL 1.1
- fixed a possible crash if sftp stat gets an unexpected response
- fixed incorrect parsing of the KEX preference string value
- fixed conditional RSA and AES-CTR support
- fixed a small memory leak during the key exchange process
- fixed a possible memory leak of the ssh banner string
- fixed various small memory leaks in the backends
- fixed possible out of bounds read when parsing public keys from the server
- fixed possible out of bounds read when parsing invalid PEM files
- no longer null terminates the scp remote exec command
- now handle errors when diffie hellman key pair generation fails
- fixed compiling on Windows with the flag STDCALL=ON
- improved building instructions
- improved unit tests