Cleaned up build script script comment.
Suppress "unused variable" warning for external CMake project also.
Change CMake library type preferences to agree with Urho3D.

This change helps external CMake project to choose the correct library type as the compiler flags setup by the Urho3D-CMake-Magic module. Both the external project and the cmake module are being governed by the same URHO3D_LIB_TYPE build option.