Error in Masked Table documentation (or in behavior of masked Tables)

Note: this is *not* a duplicate of #1339 

The documentation for masked tables (both the 0.2.4 and the 0.3dev versions) states that (emphasis added):

> The actual mask for the table as a whole or a single column can be viewed **and modified** via the `mask` attribute

While it is true that the mask for the entire table can be *viewed* with the `mask` attribute, it cannot be modified.

As far as I can tell only column masks can be modified using the `mask` attribute.