patch: extract fs access from patchfile into fsbackend...
patch: extract fs access from patchfile into fsbackend
Most filesystem calls are already isolated in patchfile but this is not enough:
renames are performed before patchfile is available and some chmod calls are
even done outside of the applydiff call. Once all these calls are extracted
into a backend class, we can provide cleaner APIs to write to a working
directory context directly into the repository.