ENH: #3335 Pivot table support for setting name of margins column.
ref #3335.

Adds margin_column parameter to pivot_table so that user can set it to
something other than 'All'.
Raises ValueError exception if there is a conflict between the value of
margin_column and one of the other values appearing in the indices of
the pivot table.

this is ok. in general, try to avoid reformatting other text unless its germane as its hard to see what you are changing. If you want to reformat, pls do that in a separate PR.
 can you rebase / update
 @lexual can you rebase / update
 closing, but if you'd like to update, pls reopen
 Hi, I've got some availability again to try and help out again.

I'll see if I can rebase this and try again.
 Doesn't appear I can re-open though.

Maybe I have to open a brand new one ??
