Use system_raw in ptshell

Closes gh-9391

We were using system_piped, which runs processes through pexpect. Within
the terminal, we can use system_raw, which lets the child processes
interact directly with the terminal we're running in.

IPython/terminal/ptshell.py

@@ -400,5 +400,10 b' class TerminalInteractiveShell(InteractiveShell):'
             return False
         return True
 
+    # Run !system commands directly, not through pipes, so terminal programs
+    # work correctly.
+    system = InteractiveShell.system_raw
+
+
 if __name__ == '__main__':
     TerminalInteractiveShell.instance().interact()