Case insensitive regular expression filter in MariaDB

[Afshin Mehrabani]

Hello,

I have noticed an issue in my local machine and wanted to open a PR but I thought it's better to confirm this with you guys first.

I'm using MariaDB and tried to use iregex but noticed that it doesn't work at all. After adding `(?i)` to the beginning of the regex, I managed to filter the results in a case-insensitive way.

See https://mariadb.com/kb/en/library/pcre/ for more Regex options.

I'm using:

mysql  Ver 15.1 Distrib 10.2.10-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2

Let me know what you think. I can open a PR.

Thanks

[Tim Graham]

Django doesn't have official support or testing with MariaDB. It's proposed at https://groups.google.com/d/topic/django-developers/31j1dNOZ7zc/discussion.