Merge tag 'v1.4.1rc1' into develop

Synapse 1.4.1rc1 (2019-10-17)
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Bugfixes
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- Fix bug where redacted events were sometimes incorrectly censored in the database, breaking APIs that attempted to fetch such events. ([\#6185](https://github.com/matrix-org/synapse/issues/6185), [5b0e9948](https://github.com/matrix-org/synapse/commit/5b0e9948eaae801643e594b5abc8ee4b10bd194e))