block_histogram: de-globalize some variables.
block_histogram: de-globalize some variables.

wjcjenny/dailygraphics,abcnews/dailygraphics,nprapps/dailygraphics,nprapps/dailygraphics,swastvedt/dailygraphics,onyxfish/dailygraphics,onyxfish/dailygraphics,wjcjenny/dailygraphics,BenHeubl/dailygraphics,abcnews/dailygraphics,BenHeubl/dailygraphics,onyxfish/dailygraphics,stlpublicradio/dailygraphics,louisstow/dailygraphics,nprapps/dailygraphics,abcnews/dailygraphics,swastvedt/dailygraphics,stlpublicradio/dailygraphics,wjcjenny/dailygraphics,nprapps/dailygraphics,swastvedt/dailygraphics,stlpublicradio/dailygraphics,cerealcommas/mashgraphics,cerealcommas/mashgraphics,cerealcommas/mashgraphics,louisstow/dailygraphics,BenHeubl/dailygraphics,louisstow/dailygraphics,stlpublicradio/dailygraphics,abcnews/dailygraphics