src/channel.scm (channel-set-pty-size!): New procedure.

* src/channel-func.h: Add `guile_ssh_set_set_pty_size_x'.
* src/channel-func.c (guile_ssh_channel_set_pty_size_x): New
  procedure.
* src/channel.scm: Export `channel-set-pty-size!'.