add cmake flag BUILD_PYTHON for en- and disabling python extensions .
add missing if-guard for suppressing debug output in MBSGD.cpp.
OPENMP link flags are already set some lines above.
use relative path for documentation installation based on CMAKE_INSTALL_PPREFIX
implicitly.
let pkgconfig file be installed to CMAKE_INSTALL_PREFIX/lib/pkgconfig.
(CMAKE_INSTALL_PREFIX is set automatically for install command).
Merge branch 'master' of github.com:/Ruun/OpenANN