Hi,

A substantial fraction of times when exporting my org-babel document
(with many R session code blocks), I get "code block produced no
value".  I think this is because of a race condition between
waiting for the transfer.file to exist and actually populating it with
output; the scenario is: 1. write.table() creates its output file
2. emacs notices its existence, and reads it 3. write.table() gets round
to writing .Last.value to the file.

The attached patch has made exporting much more reliable for me.