ROOTCOREDIR -> ROOTCOREBIN

ROOTCOREBIN is the directory from which we pick up the /data/* files.
ROOTCOREBIN and ROOTCOREDIR usually point to the same directory.
However, starting from RootCore-00-02-80 (pulled in by
SUSYTools-00-03-21), we see that some of the grid jobs cannot access
files through ROOTCOREDIR.
Merge pull request #13 from gerbaudo/fix-rootcore-bin

ROOTCOREDIR -> ROOTCOREBIN