Fix mistake that would build qpOASES even if BLAS is not found.
First attempt to make it possible to build a dll on windows.

Windows seems to need to have dependencies available when linking dll files.
Add some dependencies needed, and rearrange the add_subdirectory invocations
in the root CMakeLists.txt to respect the dependency order.
Merge pull request #847 from toivoh/windows_dll

First attempt to make it possible to build CasADi as dlls on windows