stabletailgraph: add test cases challenging the open merge stack
This adds three more complex test cases with situations requiring tricky
state update in the stack-based iteration (arriving soon).
#!/usr/bin/env python3
import errno
import os
import sys
for f in sys.argv[1:]:
try:
print(f, '->', os.readlink(f))
except OSError as err:
if err.errno != errno.EINVAL:
raise
print(f, '->', f, 'not a symlink')
sys.exit(0)