Avoid race condition in ob-R code responsible for writing result to disk

Slight modification of patch by Christophe Rhodes

* lisp/ob-R.el (org-babel-R-write-object-command): Ensure that all
  data is written to the results file before Emacs notices that the file
  exists.

lisp/ob-R.el

@@ -227,7 +227,7 @@ current code buffer."
 (defvar org-babel-R-eoe-indicator "'org_babel_R_eoe'")
 (defvar org-babel-R-eoe-output "[1] \"org_babel_R_eoe\"")
 
-(defvar org-babel-R-write-object-command "{function(object, transfer.file) {object;invisible(if(inherits(try(write.table(object, file=transfer.file, sep=\"\\t\", na=\"nil\",row.names=%s, col.names=%s, quote=FALSE), silent=TRUE),\"try-error\")) {if(!file.exists(transfer.file)) file.create(transfer.file)})}}(object=%s, transfer.file=\"%s\")")
+(defvar org-babel-R-write-object-command "{function(object,transfer.file){object;invisible(if(inherits(try({tfile<-tempfile();write.table(object,file=tfile,sep=\"\\t\",na=\"nil\",row.names=%s,col.names=%s,quote=FALSE);file.rename(tfile,transfer.file)},silent=TRUE),\"try-error\")){if(!file.exists(transfer.file))file.create(transfer.file)})}}(object=%s,transfer.file=\"%s\")")
 
 (defun org-babel-R-evaluate
   (session body result-type column-names-p row-names-p)