PreRunChain functions run in the order of root to child.
PostRunChain functions run in the order of child to root.

The overall exection order for a command is
PreRunChain
PersistentPreRun
PreRun
Run
PostRun
PersistentPostRun
PostRunChain

The following gist describes the usage and functionality
https://gist.github.com/algrebe/23cc8bf4739a129a6d0d

This reverts commit 3dbb5be.
As part of spf13#220
PreRunChain and PostRunChain aren't required - the PersistentRun functions
need to be modified

Added the functionality for persistent functions to chain
from root to child in the case of PersistentPreRun and
from child to root in the case of PersistentPostRun.

Added a global internal variable useChainHooks which decides
whether to use chain feature, or use the previous logic of nearest
defined ancestor.
This variable useChainHooks is disabled by default in this commit.
Developers importing the cobra package can enable it using the
function EnableChainHooks() or disable it using DisableChainHooks().
However, these functions may be called only once externally, preferably
in the init of the developers main program.