Table > value should not work

In Python 2, the following works:

```
In [1]: from astropy.table import Table

In [2]: t = Table([[1,2,3]])

In [3]: t > 0.2
Out[3]: True
```

but I think it shouldn't, and indeed doesn't in Python 3:

```
In [1]: from astropy.table import Table

In [2]: t = Table([[1,2,3]])

In [3]: t > 0.2
ERROR: TypeError: unorderable types: Table() > float() [IPython.core.interactiveshell]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-3-26baf2ef9239> in <module>()
----> 1 t > 0.2

TypeError: unorderable types: Table() > float()
```

The Python 2 behavior led me to confusion when I did ``t[t > 0.2]`` by mistake, when I meant ``t[t['RA'] > 0.2]``.