libssh2 1.4.0

This release includes the following changes:

 o Added libssh2_session_supported_algs()
 o Added libssh2_session_banner_get()
 o Added libssh2_sftp_get_channel()
 o libssh2.h: bump the default window size to 256K

This release includes the following bugfixes:

 o sftp-seek: clear EOF flag
 o userauth: Provide more informations if ssh pub key extraction fails
 o ssh2_exec: skip error outputs for EAGAIN
 o LIBSSH2_SFTP_PACKET_MAXLEN: increase to 80000
 o knownhost_check(): Don't dereference ext if NULL is passed
 o knownhost_add: Avoid dereferencing uninitialized memory on error path
 o OpenSSL EVP: fix threaded use of structs
 o _libssh2_channel_read: react on errors from receive_window_adjust
 o sftp_read: cap the read ahead maximum amount
 o _libssh2_channel_read: fix non-blocking window adjusting

This release would not have looked like this without help, code, reports and
advice from friends like these:

 Gellule Xg, Jernej Kovacic, Peter Krempa, Vincent Torri, Kamil Dudka,
 Peter Stuge, Guenter Knauf, John Engstrom, Alexander Lamaison,
 Mikhail Gusarov
 
        Thanks! (and sorry if I forgot to mention someone)