consolidate dump traces to a single string before printing
consolidate dump traces to a single string before printing

When running multithreaded, several actors might be printing
dump messages simultaneously. To prevent the messages from
getting comingled to the point of unreadability, build a single
string and use #print to print it. A quirk of IO#print is that
it it not interruptible so each message printed is completed
before another string can be processed.

kenichi/celluloid,dilumn/celluloid,sideci-sample/sideci-sample-celluloid,seuros/celluloid,olleolleolle/celluloid,celluloid/celluloid,marshall-lee/celluloid,davydovanton/celluloid,jstoja/celluloid,jasonm23/celluloid,TiagoCardoso1983/celluloid,mehta/celluloid