Invalid system date causes downloads to fail with cryptic message

Set your system date to somewhere in past (in my case it was 26 July 2015)
Try to install app from F-Droid.
It fails with message "Not installed".

Source issue: SSL certificate is rejected because it comes from future.

Expected behaviour: user should see message "SSL certificate rejected", "Invalid SSL certificate", "Certificate from future, check your system date" or similar.

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