Add mine_functions section to minion config

[tmandry]

See http://docs.saltstack.com/topics/mine/ for details.

I needed this in order to use the hostsfile-formula.

[wwentland]

It would be great if you, @tmandry, could add an example of this functionality to pillar.example.

Can you think of a way to allow for support of mine function aliases in the future (or now) in such a way that existing pillars remain backwards compatible? If you can it would be great if this PR could be updated accordingly as it would be a shame if we have to introduce backward incompatible changes once Helium has been released in order to support that functionality.

[jcftang]

@nmadhok given that #91 got reverted due to my mistake, is there a possibility of getting this merged? is there something fundamentally broken with this PR?

[iggy]

A. It contains merge conflicts
B. You are putting something in a pillar to then have it loaded into a config file when it can be read from the pillar to begin with

[nmadhok]

@jcftang Like @iggy mentioned in a comment above, this PR contains merge conflicts and you need to resolve the merge conflicts first so I can consider it further.

[jcftang]

Ok, it feels like it's better to note to the user it is better to put this config into the minion pillar first before trying to resolve the conflict. I'm adding a link here to the documentation -- http://docs.saltstack.com/en/latest/topics/mine/#mine-functions

[aboe76]

Only thing that can be set only in the minion config is the mine interval
the mine_interval must be set in the minion’s runtime config.
The configuration option is ignored in grains or pillar data.