Update gtk-demo MSVC Projects

* MSVC_Net2005/demos/gtk-demo/gtk-demo.vcproj:
  MSVC_Net2008/demos/gtk-demo/gtk-demo.vcproj:
  MSVC_Net2010/demos/gtk-demo/gtk-demo.vcxproj: Use _fgetc_nolock as a
  direct MSVC replacement for getc_unlocked, as this is what Microsoft
  compilers use for the same purpose.  This will fix the build of the
  demos projects without needing to replace getc_unlocked() with getc(),
  which is not an accurate replacement of getc_unlocked() anyways.