Fixes linker issues when linking statically to lua on Windows platforms as required by VisualStudio.  This should probably be resolved by making Vector2f and Vector2i opaque from outside of libRocket Core rather than exposing the templates outside of libRocket.  Keeping the classes opaque would allow the implementation to change in a shared library without requiring the application to be recompiled to pickup the changes.  This fixes #199.
Merge branch 'hotfix/issue-199' into stable