[automation.py] Use WinDLL instead of OleDLL

Only to have a more consistent code because we always use WinDLL

comtypes/automation.py

@@ -575,23 +575,27 @@ def ChangeType(self, typecode):
 VARIANT = tagVARIANT
 VARIANTARG = VARIANT
 
-_oleaut32 = OleDLL("oleaut32")
+_oleaut32 = WinDLL("oleaut32")
 
 _VariantChangeType = _oleaut32.VariantChangeType
 _VariantChangeType.argtypes = (POINTER(VARIANT), POINTER(VARIANT), c_ushort, VARTYPE)
+_VariantChangeType.restype = HRESULT
 
 _VariantClear = _oleaut32.VariantClear
 _VariantClear.argtypes = (POINTER(VARIANT),)
+_VariantClear.restype = HRESULT
 
-_SysAllocStringLen = windll.oleaut32.SysAllocStringLen
+_SysAllocStringLen = _oleaut32.SysAllocStringLen
 _SysAllocStringLen.argtypes = c_wchar_p, c_uint
 _SysAllocStringLen.restype = c_void_p
 
 _VariantCopy = _oleaut32.VariantCopy
 _VariantCopy.argtypes = POINTER(VARIANT), POINTER(VARIANT)
+_VariantCopy.restype = HRESULT
 
 _VariantCopyInd = _oleaut32.VariantCopyInd
 _VariantCopyInd.argtypes = POINTER(VARIANT), POINTER(VARIANT)
+_VariantCopyInd.restype = HRESULT
 
 # some commonly used VARIANT instances
 VARIANT.null = VARIANT(None)