DataFrame append locks appear to work now.
DataFrame append locks appear to work now.

Not sure how, exactly, but the write locks on append appear to be
working. They don't work well, however, when multiple processes
are trying to append to a file that doesn't yet exist. This should
be addressed yet.

dotsdl/datreant,andreabedini/datreant,datreant/datreant.data,datreant/datreant,datreant/datreant.core,datreant/datreant.core,datreant/datreant