opt out of accursedUnutterablePerformIO

[Ben Franksen]

Am 06.03.2018 um 22:28 schrieb Bertram Felgenhauer via Libraries:
> This has nothing to do with <insane>PerformIO.
> [...]
> You are kind of lucky that linesPS1 works.

Thanks a lot! I did not know that bytestring uses a null pointer for an
empty buffer. Clever. And you somewhat restored my belief in the safety
of bytestring. This use of the Data.ByteString.Internal is indeed unsafe
but for quite humanly understandable reasons and the whole
<whatever>PerformIO was a red herring. I have already written a new
version of betweenLinesPS that uses breakSubstring (not available back
then) and it is now perfectly safe. I have also added a ticket to remind
us to review (purge, if possible) all uses of the Internal BS API.

Cheers
Ben