Changes to make NVDA work again on Windows XP with no service pack:

Changes to make NVDA work again on Windows XP with no service pack:
	* NVDAHelper: winIPCUtils: generateDesktopSpecificNamespace(): wcscpy_s() isn't available in Windows XP no sp, so use wcsncpy() instead.
	* IAccessible NVDAObject: findOverlayClasses(): msftedit.dll isn't available on Windows XP no sp, so handle this gracefully when trying to retrieve IID_ITextServices. Also, only ever attempt to retrieve it once and cache the result for later use, which should be more efficient.

Fixes #908.