RemoteFile can read local file now; remove now redundant code
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Fixes #11764 part 2
Fix occasional crash on startup OS 10.9
Add ability to disable IPv6 without recompiling

This fix an issue on having the backend IPv6 address always set which could prevent some clients to connect
Delete file if its creation failed

It would otherwise leave 0 bytes files and would prevent the images to ever be downloaded again...
The code is in triplicate when only one case is required.. to be done post 0.27