Fix wrong include flags for building python extension

Fix an error that made the include paths for building the python
extension incorrect, which resulted in missing numpy headers on Mac OS.

src/python/wscript

@@ -52,7 +52,7 @@ def build(ctx):
         source   = ctx.path.ant_glob('essentia.cpp parsing.cpp pytypes/*.cpp'),
         target   = '_essentia',
         features = 'pyext',
-        includes = NUMPY_INCPATH + [ '.', 'pytypes' ] + ctx.env.INCLUDES_ESSENTIA if ctx.env.ONLY_PYTHON else adjust(ctx.env.INCLUDES, '..'),
+        includes = NUMPY_INCPATH + [ '.', 'pytypes' ] + (ctx.env.INCLUDES_ESSENTIA if ctx.env.ONLY_PYTHON else adjust(ctx.env.INCLUDES, '..')),
         cxxflags = [ '-w' ],
         install_path = '${PYTHONDIR}/essentia',
         use      = ctx.env.USE_LIBS if ctx.env.ONLY_PYTHON else 'essentia ' #+ ctx.env.USE_LIBS