[FR-devel] alias of a couple of methods

[Rich Kilmer]

I aliased these methods:

slot.data => slot.value

slot.call(...) => slot.invoke(...)

Of course the old methods still work.  I did this because I think that
in some code .value would be clearer than .data and the same with .call
and .invoke.  To learn from Ruby itself, aliases are not bad to have if
it makes code clearer.

-rich