mariadb: security bump to 10.2.19

mariadb: security bump to 10.2.19

Many, many bug fixes, see release notes for details:
https://mariadb.com/kb/en/library/mariadb-10219-release-notes/

Fixed CVEs:

  CVE-2018-3282
  CVE-2016-9843
  CVE-2018-3174
  CVE-2018-3143
  CVE-2018-3156
  CVE-2018-3251
  CVE-2018-3185
  CVE-2018-3277
  CVE-2018-3162
  CVE-2018-3173
  CVE-2018-3200
  CVE-2018-3284

OpenWrt package changes:

  - include sha256_password in libmariadb package
  - upstream provided new pkgconfig file libmariadb.pc
  - refreshed one patch, dropped two others (included in upstream source
    now)

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>