In chg's case, making modules lazily loaded could actually slow down things
since chg pre-imports them. Therefore disable demandimport if chg is being
used.
This is not done by setting `HGDEMANDIMPORT` chg client-side because that
has side-effects on child processes (hooks, etc).
Differential Revision: https://phab.mercurial-scm.org/D351
In general, the attribute of the same name is overwritten by executing an
import statement.
import a.b
print(a.b.c) # 'c' of a/b/__init__.py
from a.b.c import d
print(a.b.c) # a/b/c.py
However, this appears not true for the scenario described in the test case,
and surprisingly, "from a.b.c import d" works even if "a.b.c" is not a module.
This patch works around the problem by taking the right module from sys.modules
if available.
