graphmod: correctly emit nodes with more than 2 predecessors
The grandparent() function was returning only the closest predecessor of a
missing parent while it must return all of them to display a correct ancestry
graph.
#!/usr/bin/env python
# Filter output by the progress extension to make it readable in tests
import sys, re
for line in sys.stdin:
line = re.sub(r'\r+[^\n]', lambda m: '\n' + m.group()[-1:], line)
sys.stdout.write(line)
print