Change TERM from msys to cygwin.

Set `TERM=cygwin` as that actually exists in common terminfo databases.
msys is a fork of cygwin so this is definitely the most compatible thing to do.

`msys` is a loose alias for `cygwin` in msysgit. From the [msysgit termcap](https://github.com/msysgit/msysgit/blob/master/etc/termcap#L165):
```
cygwin:\
        :xn@:op=\E[39;49m:Km=\E[M:tc=linux:

msys:\
        :xn@:op=\E[39;49m:Km=\E[M:tc=linux:tc=rxvt:
```

Not sure what the purpose of the addition is here. It just adds mostly eccentric capabilities that `cmd` does not support.
It used to be a direct alias in the past.

```
$ infocmp -L msys cygwin
comparing msys to cygwin.
    comparing booleans.
        has_meta_key: T:F.
    comparing numbers.
    comparing strings.
        cursor_visible: '\E[?25h', NULL.
        enter_ca_mode: '\E7\E[?47h', NULL.
        exit_ca_mode: '\E[2J\E[?47l\E8', NULL.
        init_1string: '\E[?47l\E=\E[?1l', NULL.
        init_2string: '\E[r\E[m\E[2J\E[H\E[?7h\E[?1;3;4;6l\E[4l', NULL.
        key_a1: '\EOw', NULL.
        key_a3: '\EOy', NULL.
        key_c1: '\EOq', NULL.
        key_c3: '\EOs', NULL.
        key_f0: '\E[21~', NULL.
        keypad_local: '\E>', NULL.
        keypad_xmit: '\E=', NULL.
        parm_down_cursor: '\E[%p1%dB', NULL.
        parm_left_cursor: '\E[%p1%dD', NULL.
        parm_right_cursor: '\E[%p1%dC', NULL.
        parm_up_cursor: '\E[%p1%dA', NULL.
```

Of course, one could also just install the msys entry to the server being SSHed into:
```
$ wget https://raw.github.com/msysgit/msysgit/master/etc/termcap
$ tic -e msys termcap
```

Would close #44, #50, and #56.