[debian-mysql] Bug#848603: Enable innodb_large_prefix

[Clint Byrum]

Excerpts from Otto Kekäläinen's message of 2016-12-19 23:20:49 +0200:
> Severity: normal
> 
> We live in a world where WordPress sites expect to be able to save
> emojis in comments :)
> 
> We have had utf8mb4 as default in Debian and Ubuntu for a many years.
> You are experiencing a corner case with a single app (which one?).
> 

Also it's worth noting that you probably _don't_ want to make an
index 255*3 bytes, as it will perform horribly and take up a ton of
extra space. Users should consider VARBINARY if it's a giant key that
doesn't require sorting, or setting the charset of that specific field to
something that accomodates the content, but indexes efficiently (latin1,
for instance, works if you only have ASCII).