SF bug #438295: [Windows] __init__.py cause strange behavior

SF bug #438295: [Windows] __init__.py cause strange behavior
Probable fix (the bug report doesn't have enough info to say for sure).
find_init_module():  Insist on a case-sensitive match for __init__ files.
Given __INIT__.PY instead, find_init_module() thought that was fine, but
the later attempt to do find_module("__INIT__.PY") didn't and its caller
silently suppressed the resulting ImportError.  Now find_init_module()
refuses to accept __INIT__.PY to begin with.
Bugfix candidate; specific to platforms with case-insensitive filesystems.