BUG: Bug in fillna with limit and value specified
from SO: http://stackoverflow.com/questions/22379343/change-first-occurrence-of-nan-in-a-specific-dataframe-row-to-a-new-value/22380225#22380225

Looks good to me.
 thanks....Panel is now NotImplemented, because its ambiguous which direction to run the limit filling. Not sure how to deal with it (as really need another argument I think).
