Remove variable output affected by length of TMPDIR.
If the temporary directory is longer than /tmp then it's possible that
the Subject line will get wrapped by the headencode function.
tests: update to match "hg help resolve" output from
53fdc0989047
url: limit expansion to safe auth keys (Issue2328)
Mads Kiilerich pointed out that
7c9beccb0533 was too eager since the
prefix and password keys may contain $-signs. So this only add the
username to the list of keys that are expanded.
This also updates the documentation to match.