Ssh2 build (#9)

Added libssh2 build script.
Refactor - moved agent init and auth functions to outside Session class.
Fixed double de-allocation of more than one channel from the same session.
Added session property to channel for parent session of channel.
Refactoring - made agent related functions available as Cython functions under ssh2.agent that can be cimported.
Fixed agent authentication error/exception handling.
Added authentication error handling session tests.
Added SFTPIOError exception.
Added last_errno and set_last_error session functions.
Added raising SFTPIOError on sftp mkdir errors.
Added socket object and file descriptor attributes to session object for better de-allocation of sockets and socket use via C-API.
Updated changelog.
Added bytes conversion on SFTP mkdir and mkdir test.
Re-generated C files for updated cython.
Implemented hostkey_hash session method for computing host key hash and test.
Minor code updates for performance.
Updated doc strings.
Fixed sftp readdir_ex long entry, added test. SFTP  performance improvements.

Author: pkittenis

Changelog.rst

@@ -1,11 +1,28 @@
 Change Log
 =============
 
+0.6.0
+++++++
+
+Changes
+---------
+
+* Implemented `last_errno` and `set_last_error` session functions
+* Agent authentication errors raise exceptions
+* C-API refactor
+* SFTP IO errors raise exceptions
+
+Fixes
+-------
+
+* Crash on de-allocation of channel in certain cases
+* SFTP ``readdir_ex`` directory listing (long entry) was not returned correctly
+
 0.5.5
 ++++++
 
 Changes
---------
+---------
 
 * Accept both bytes and unicode parameters in authentication with public key from memory.
 

ci/build-ssh2.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -xe
+
+mkdir -p src && cd src
+cmake ../libssh2 -DBUILD_SHARED_LIBS=ON -DENABLE_ZLIB_COMPRESSION=ON \
+    -DENABLE_CRYPT_NONE=ON -DENABLE_MAC_NONE=ON -DCRYPTO_BACKEND=OpenSSL
+cmake --build . --config Release

setup.py

@@ -24,6 +24,8 @@
 ext = 'pyx' if USING_CYTHON else 'c'
 sources = glob('ssh2/*.%s' % (ext,))
 _libs = ['ssh2'] if platform.system() != 'Windows' else [
+    # For libssh2 OpenSSL backend on Windows.
+    # Windows native WinCNG is used by default.
     # 'libeay32', 'ssleay32',
     'Ws2_32', 'libssh2', 'user32']