Restrict the types of errors that return file_exists.
Restrict the types of errors that return file_exists.

I have seen some 'file exists' error messages in the log files.  We have to make
sure these are really race conditions and not something else.

ErikDubbelboer/disco,discoproject/disco,simudream/disco,discoproject/disco,mwilliams3/disco,seabirdzh/disco,ktkt2009/disco,ErikDubbelboer/disco,mwilliams3/disco,mozilla/disco,beni55/disco,mozilla/disco,ktkt2009/disco,beni55/disco,ktkt2009/disco,discoproject/disco,oldmantaiter/disco,seabirdzh/disco,oldmantaiter/disco,simudream/disco,pombredanne/disco,ktkt2009/disco,seabirdzh/disco,oldmantaiter/disco,pooya/disco,pooya/disco,ktkt2009/disco,pombredanne/disco,oldmantaiter/disco,discoproject/disco,ErikDubbelboer/disco,mozilla/disco,beni55/disco,simudream/disco,ErikDubbelboer/disco,seabirdzh/disco,oldmantaiter/disco,seabirdzh/disco,pombredanne/disco,beni55/disco,ErikDubbelboer/disco,mozilla/disco,mwilliams3/disco,beni55/disco,mwilliams3/disco,simudream/disco,pombredanne/disco,mwilliams3/disco,pombredanne/disco,simudream/disco,discoproject/disco,pooya/disco,pooya/disco