Small fixes to pass Windows Store App Certification tests when HAVE_WINRT is enabled.

This pull request contains a few small changes that will enable apps using opencv with HAVE_WINRT enabled to pass the Windows Store App Certification tests. This changes also enables opencv to be built for Windows Phone 8.0. 

The following changes were made:

modules/core/src/ocl.cpp - WinRT apps build for the Windows Store do not have access to OpenCL. The OpenCL functions return NULL or 0 if HAVE_WINRT is defined. Also, getenv() is not available to WinRT apps and a stubbed version was added.

modules/core/src/parallel.cpp - added check for HAVE_WINRT to correctly set  HAVE_CONCURRENCY

modules/core/src/system.cpp - _wgetenv is not available to WinRT apps. Cleaned up string code compile errors for HAVE_WINRT.

modules/objdetect/src/matching.cpp - reduced the complexity of the parameters to malloc. The ARM compiles for Windows Phone 8 is not able to handle the original expressions.