posix: retry on symlink race in checklink Multiple threads might attempt to check links with the same temporary name. This would cause one side to get an EEXIST error and wrongly fail the support check. Here, we simply retry if our temporary name exists.

changegroup: back code change of e7c618cee8df out The previous changeset is a simpler way of fixing issue4934 without changing the spirit of the code. We can remove the dual call to 'delayupdate' but we keep the tests to show that the issue is still fixed.