[QA] overwriting existing files is unreliable

[jnweiger]

Seen with both files_external_dropbox 2.0.0-rc.2 and files_external_dropbox-1.2.0

• Create an 'app' in dropbox, enable all checkboxes under Individual Scopes
• Create an external folder mount with dropboxV2 and key and secret of this 'app'
• enter the external dropbox folder.
• New -> TextFile, the texteditor opens (with notably delay). OKish
• Start typing text, watch the saving status in the top row of the editor. It cycles through several messages: BAD
  
  

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• When closing the editor another yellow reminder appears.
  
• After 3 or 4 attempts (with exiting, reopening text editor, and re-typing, what is still missing) one or two lines of text can be successfully changed (in a short file).

Expected behaviour:

• As there is no other user involved, no 'locked' errors should occur.
• Retyping of lost text should not be necessary.

Performance:

• When a save will be successful, the texteditor often hangs 5 to 10 seconds in "saving..." before it switches to "Saved!".
• When unsuccessful, "saving..." is only shown for less than 2 seconds, before the error message appears.