demandimport: change default for level from None to -1
The Python default for this function is -1, indicating both relative
and absolute imports should be used.[1] Previously, we relied on the
Python VM not passing level when such semantics were
requisted. This is not the case for PyPy, however, where a level of -1
is always passed to __import__.
[1] <http://docs.python.org/library/functions.html#__import__>
$ 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