encoding: use s.decode to trigger UnicodeDecodeError
When calling encode on a str, the string is first decoded using the
default encoding and then encoded. So
s.encode('ascii') == s.decode().encode('ascii')
We don't care about the encode step here -- we're just after the
UnicodeDecodeError raised by decode if it finds a non-ASCII character.
This way is also marginally faster since it saves the construction of
the extra str object.
$ hg init
$ echo 0 > a
$ echo 0 > b
$ hg ci -A -m m
adding a
adding b
$ hg rm a
$ hg cat a
0
$ hg cat --decode a # more tests in test-encode
0
$ echo 1 > b
$ hg ci -m m
$ echo 2 > b
$ hg cat -r 0 a
0
$ hg cat -r 0 b
0
$ hg cat -r 1 a
a: no such file in rev 7040230c159c
[1]
$ hg cat -r 1 b
1