Fix cleanup to really remove 'aria_log' files. Fixes failures in maria unit tests on some platforms.
Fixed compiler warnings

include/mysql/plugin.h:
  Changed def_val back to const, to remove compiler warnings.
storage/maria/ma_init.c:
  Rename control file and log files from maria_xxx to aria_xxx when upgrading from MariaDB 5.1
storage/maria/unittest/ma_maria_log_cleanup.c:
  Fix cleanup to really remove 'aria_log' files. Fixes failures in maria unit tests on some platforms.