Doc:  Remove old versions for consistent behavior

If you have older versions of the gem also installed, this causes the
"v2" functionality to be flakey.  (From IRC with Matt Ray, tested by
me)  

Included warning and command examples to show how to check and remedy 
this situtation.
Merge pull request #29 from behemphi/master

Update doc for mulitiple knife-rackspace gem version issue and fix.