Added width_pixel and height_pixel parameters to Channel.get_pty() and
resize_pty(), and Client.invoke_shell().  Perhaps useless, but more RFC
compliant.  Updated methods to include these parameters in server messages.

Adjusted Channel.resize_pty() to neither request nor wait for a response, as
per RFC 4254 6.7 (A response SHOULD NOT be sent to this message.)  This is
necessary as certain hosts have been observed to not acknowledge this type of
channel request (Cisco IOS XR), which causes paramiko to end the session.
Changelog re #133, and date fix for 1.10