Allow recursive includes in tree (JSON) files

Prior we only allowed for one include in our json file inputs.  Now
these files can recusively include more than one.  This is handled
in the flattenjsoninclude function

taskbase.py
    - flattenjsoninclude is now recursive
    - it requires the includefile name as an arg input
This is nonideal if includefile is an absolute path. (Not that I can imagine a goodreason for someone doing that... but I can imagine bad ones). I believe that os.path.join() handles this.