• Accept debug flag on the constructor.
  
• Ensure the crypto libraries are positioned after libssh2 on
  the link line (bug report and patch by Jacques Germishuys).
  
• Channel "pty" method now accepts mode modifiers passed as a
  hash.
  
• In connect, warnif was clobbering $! (bug report and patch
  by ikegami).
  
• t/Net-SSH2.t: add support for TEST_NET_SSH2_TRACE