issue2550535 Fix keep_quoted_text=yes setting. In some cases even when keep_quoted_text=yes is configured we would strip quoted sections. This hit the python bug-tracker especially for python interpreter examples with leading '>>>' strings. The fix is slightly different compared to the proposal as this broke keep_quoted_text=no in certain cases. We also fix a bug where keep_quoted_text=no would drop the last line of a non-quoted section if there wasn't an empty line between the next quotes.

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