setup: try setup_requires

Author: tschaume

setup.py

@@ -17,6 +17,7 @@
     dependency_links = [
         'http://sourceforge.net/projects/gnuplot-py/files/Gnuplot-py/1.8/gnuplot-py-1.8.tar.gz/download'
     ],
+    setup_requires = [ 'numpy==1.9.2' ],
     install_requires = [
         'numpy==1.9.2', 'Pint==0.5.1',
         'PyModelFit==0.1.2', 'uncertainties==2.4.4'