fixed isFileExist to use full path
Merge pull request #3851 from MSOpenTech/winrt-fileutils-fix

[ci skip]Winrt fileutils fix
support for precompiled shaders on winrt/wp8
added sha1 algorithm since it is missing in WP8 SDK
added winrt precompiled shaders
removed precompiled shader code
added support for precompiled shaders
added precompiled shader support for winrt/wp8
removed old precompiled shaders
removed old WP8 precompiled shaders
added CCPreompiledShaders.h for winrt and wp8
adding loading of precompiled shader programs
removed winrt code
added CCPrecompiledShader files
added precompileShaders() for wint
added precompiledshaders.h
added PRECOMPILED_SHADERS define
added sha1 support
added CC_PLATFORM_WP8
updated winrt shaderts