context: make sure __str__ works, also when there is no _changectx
Before, it could crash when trying to print the wrong kind of object at the
wrong time.
largefiles: clarify variable name holding file mode
A follow-up to
c01acee367ec.
'st' sounds like the whole stat result while 'mode' is a better name for the
actual file mode.
changegroup: use changelogrevision()
Using offsets for accessing changelog entries isn't very readable.
As a bonus, changelog.changelogrevision() also accepts a revision,
so we don't need to perform the inline node resolution either.