tests: enable import checker for all **.py files

Several known-bad files are excluded as they couldn't be trivially fixed.
That's the same as 99a2bdad0fda.

tests/test-check-module-imports.t

@@ -155,8 +155,12 b' these may expose other cycles.'
 Known-bad files are excluded by -X as some of them would produce unstable
 outputs, which should be fixed later.
 
-  $ hg locate 'mercurial/**.py' 'hgext/**.py' 'tests/**.py' \
+  $ hg locate '**.py' \
   > 'tests/**.t' \
+  > -X contrib/debugshell.py \
+  > -X contrib/win32/hgwebdir_wsgi.py \
+  > -X doc/gendoc.py \
+  > -X doc/hgmanpage.py \
   > -X tests/test-hgweb-auth.py \
   > -X tests/hypothesishelpers.py \
   > -X tests/test-ctxmanager.py \