fix error reporting in setup.py

--HG--
extra : rebase_source : 7d2bd536e8421de06cdffaa2d2bd1e8f158ac8d5
fix several issues in setup.py and make pkgconfig evaluation more Py3 compatible

--HG--
extra : rebase_source : ba06ec7166cae40cb8eae5cddce5e91749f8d694
only use Cython on explicit request or when generated sources are missing

--HG--
extra : rebase_source : 5316a0dd7121f56488e202892ed6c889bdc5aed7
be smarter about decoding pkgconfig output in setup.py

--HG--
extra : rebase_source : 25563e4a33ce3fa9d352da68bb7ddb7f81fab6aa
fix last commit