WP8 fixes for v3.3 app certification tests

This pull requests fixes issues that caused it to fail the Windows Store App Certification tests

1. Fixed banned win32 API calls in CCFileUtils.cpp. Note: Win32 methods ending with A are banned. I defined UNICODE to enforce the banning of A functions instead of W.
2. Refactored CCFileUtils.cpp to better handle checks for CC_TARGET_PLATFORM
3. Fixed incorrect property sheet in WP8 libcocos2d project
4. Updated the WP8 precompiled shaders