Put numpy into a pre.txt so that everything will actually install.

rakefiles/prereqs.rake

@@ -31,6 +31,7 @@ task :install_python_prereqs => "ws:migrate" do
     unchanged = 'Python requirements unchanged, nothing to install'
     when_changed(unchanged, 'requirements/**/*') do
         ENV['PIP_DOWNLOAD_CACHE'] ||= '.pip_download_cache'
+        sh('pip install --exists-action w -r requirements/edx/pre.txt')
         sh('pip install --exists-action w -r requirements/edx/base.txt')
         sh('pip install --exists-action w -r requirements/edx/post.txt')
         # Check for private-requirements.txt: used to install our libs as working dirs,

requirements/edx/base.txt

@@ -29,7 +29,6 @@ mako==0.7.3
 Markdown==2.2.1
 networkx==1.7
 nltk==2.0.4
-numpy==1.6.2
 paramiko==1.9.0
 path.py==3.0.1
 Pillow==1.7.8

requirements/edx/pre.txt

+# Numpy and scipy can't be installed in the same pip run.
+# Install numpy before other things to help resolve the problem.
+numpy==1.6.2