merge: add stubs for preprocess and conclude steps of merge driver
The exact semantics for what should happen (particularly with respect to error
handling) are still a bit hard to pin down, so I think it's better to
experiment with it as an extension for now. For now this stub will act as a
convenient point for extensions to hook on.
#!/usr/bin/env python
import errno, os, 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, 'not a symlink'
sys.exit(0)