[QA] Win10 local file name clash leads to permanent error state

[jnweiger]

Test on Win10 Pro 20H2
https://download.owncloud.com/desktop/ownCloud/testing/2.7.4-rc1.2909/win/ownCloud-2.7.4-rc1.2909.x64.msi

• Trhough the web UI of demo.owncloud.org upload x_inkscape.png and x_INKSCAPE.png

• connect the client to demo.owncloud.org using VFS

• it starts syncing down and fails: BAD
  
  This error message does not convey the name clash. It appears to say that a file caused a conflict from e.g. a local modification that windows would not want to overwrite.

• disable VFS.

• the client retries syncing and fails with somewhat nicer error message:
  
  Confusing details: What is the difference between 'cannot be saved' and 'can not be downloaded' for the end user?
  (Grammer: 'cannot' is correct here. 'can not' isn't.)

The sync history was

Expected behaviour:

• both VFS and non VFS have the same error message.
• conflict resolution should be applied. both files should be available locally, one named with ...(conflict...)

Workaround: Rename the clashing file. Then the second copy gets synced down.
Note that this workaround is not feasable, when it happens multiple times in deep trees, as e.g. in the Linux kernel source tree attempted in #8318

[jnweiger]

Confirmed fixed with 2.7.5RC2
(except for the grammer detail -> #8375 )