tests/test-merge-symlinks.hg

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__>

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