termio.py:  Added a new attribute: `MultiplexPOSIXIOLoop.shell_command`.  It controls what command is used to execute commands.  By default it is, `["/bin/sh", "-c"]` but you can override it with a string or a list of your choosing *after* the Multiplex instance is created.  so that'd be: `m = Multiplex('some_command.sh'); m.shell_command = '/bin/bash -c'`
app_terminal.py:  Added a new setting you can add to your 50terminal.conf to override the default "/bin/sh -c" command that's used to execute all terminal commands.  It modifies the `Multiplex.shell_command` described above.  You can use a string or a list in the `shell_command` setting (in 50terminal.conf).