Merge pull request #161 from zachriggle/gdb-attach-warning

Add warning message.  Closes #160
Merge pull request #155 from zachriggle/tmux

run_in_new_terminal now behaves as per documentation; also can launch new tmux panes
Make ssh_channel.interactive() work when term_mode is not active
Use a proper threading.Event for synchronization rather than a list
Merge branch 'ssh-interactive-repl'