Fixed mingw cross compiler issues.
Fixed building simple opengl texture example with mingw.
Removed unreferenced variables.
Fixed class attribute initialization order.
Fixed variable assignment values.
Removed noops and warnings on unused variables.
Added conditions for compiler oder build mode dependend code.
Added parenthesis for explicit operator evaluation priority.
Replaced function parameters with correct literals.
Removed invalid extern keyword.
Merge pull request #185 from adrianbroher/master

Fix various errors and warnings that prevented build assimp_view as linux to win32 cross compile.