pegasus-kickstart: Grab the last N bytes of stdio
pegasus-kickstart: Grab the last N bytes of stdio

This commit changes the behavior of the -B option so that it grabs the
last N bytes of stdio instead of the first N bytes of stdio if the
size of stdio is larger than the -B option.

pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus,pegasus-isi/pegasus