[dovecot/core] fa4f8f: dict-sql: Cache reading settings files.

[GitHub]

  Branch: refs/heads/master-2.2
  Home:   https://github.com/dovecot/core
  Commit: fa4f8f36b213d233e25f628f48a8f3b33d842b88
      https://github.com/dovecot/core/commit/fa4f8f36b213d233e25f628f48a8f3b33d842b88
  Author: Timo Sirainen <timo.sirainen at dovecot.fi>
  Date:   2016-05-12 (Thu, 12 May 2016)

  Changed paths:
    M src/lib-dict/dict-sql-settings.c
    M src/lib-dict/dict-sql-settings.h
    M src/lib-dict/dict-sql.c

  Log Message:
  -----------
  dict-sql: Cache reading settings files.

The settings were read for every dict init, which was done for every new
dict connection. This was using a lot of CPU. There are usually only a
couple dict-sql settings files, so we cache all of the ones we read.