Extend module reimport test to also try reimports without knowing the package.

tests/run/reimport_from_package.srctree

+# mode: run
+# tag: pep489
+
 PYTHON setup.py build_ext --inplace
 PYTHON -c "import a"
 
@@ -35,6 +38,7 @@ assert sys.modules['atest.package.module'] is module, list(sys.modules)
 
 if sys.version_info >= (3, 5):
     from . import pymodule
+    assert module is pymodule.import_without_package()
 
 ######## atest/package/pymodule.py ########
 
@@ -43,3 +47,13 @@ from ..package import module
 import atest.package.module
 
 import a
+
+def import_without_package():
+    import os.path
+    import sys
+    sys.path.insert(0, os.path.dirname(__file__))
+    sys.path.insert(0, os.path.dirname(os.path.dirname(__file__)))
+    import module
+    import package.module
+    assert package.module is module
+    return module