test-bisect: fix shell-dependent output

change 'journal already exists' to 'abandoned transaction found' Journal already exists is a pretty internal piece of information, which doesn't necessarily mean much to people who are not familiar with the code. The new text is a more well-known concept.

verify: report existence of journal

bisect: no need to save the state if it wasn't changed

record: get the right position (account for skipped files)

log --limit: break after a limited number of csets (broken by f3d60543924f)

transaction: more specific exceptions, os.unlink can raise OSError

lock: catch specific exceptions

patch: use the public ctx API instead of the internals

patch: don't use mutable object as default argument

patch: initialize all attributes of the hunk class

patch: simplify logic