Switch redis.c plugin from credis to hiredis.

Switch redis.c plugin from credis to hiredis.

Change the entire redis.c plugin to use libhiredis (tested with
libhiredis0.10) instead on credis. The libhiredis is supported in a number
of distributions like Debian or Ubuntu.

This patch keeps the same functionality that the old redis.c does.

Conflicts:
	src/redis.c
	src/types.db