`cache_alias` option is not respected in FunctionJob and cacheback decorator

[Kobold]

Just that, if you pass the cache_alias option to a FunctionJob (and hence the cacheback decorator), the resulting function won't respect it. The reason why is because FunctionJob's super __init__ is called before self.cache_alias is set:

django-cacheback/cacheback/jobs.py

Lines 16 to 22 in 890772b

	super(FunctionJob, self).__init__()
	if lifetime is not None:
	self.lifetime = int(lifetime)
	if fetch_on_miss is not None:
	self.fetch_on_miss = fetch_on_miss
	if cache_alias is not None:
	self.cache_alias = cache_alias

But of course, FunctionJob's super __init__ depends on self.cache_alias, so it's too late to influence the initialization of the cache.

I'm actually responsible for this bug, so I'll also submit a PR. 🙂

[iurisilvio]

My PR fix that too.

#101