Run pip wheel -r over all requirement files in travis

Since both the demo and the migrations test use psycopg2 we might as
well build these as wheels. Should probably speed up travis runs

.travis.yml

@@ -35,12 +35,13 @@ env:
         - DJANGO=Django==1.8.1
 
 before_install:
+    # Before installation, we'll run ``pip wheel``, this will build wheels for
+    # anything that doesn't already have one on PyPI.
+    - ls requirements*.txt | xargs -n 1 pip wheel --allow-external django-oscar --process-dependency-links -r 
     - pip install codecov
 
+
 install:
-    # Before installation, we'll run ``pip wheel``, this will build wheels for
-    # anything that doesn't already have one on PyPI.
-    - pip wheel -r requirements.txt
     # Actually install our dependencies now, this will pull from the directory
     # that the first command placed the Wheels into.
     - pip install -e . -r requirements.txt $DJANGO 

requirements_demo.txt

@@ -4,7 +4,7 @@ django-oscar-paypal==0.9.1
 django-oscar-datacash==0.8.3
 
 # We need PostGIS as the stores extension uses GeoDjango.
-psycopg2==2.5.1
+psycopg2==2.6
 
 # To use Solr, we need pysolr
 pysolr==3.2

requirements_migrations.txt

@@ -1,3 +1,3 @@
 # Those dependencies are needed for the test_migrations.sh script
 PyMySQL==0.6.2
-psycopg2==2.4.5
+psycopg2==2.6