Merge pull request numpy#2769 from njsmith/fix-travis-reinstall

FIX: Use 'pip' for travis build

.travis.yml

@@ -45,7 +45,16 @@ before_install:
   - python -V
   - popd
 install:
-  - python setup.py install
+  # We used to use 'setup.py install' here, but that has the terrible
+  # behaviour that if a copy of the package is already installed in
+  # the install location, then the new copy just gets dropped on top
+  # of it. Travis typically has a stable numpy release pre-installed,
+  # and if we don't remove it, then we can accidentally end up
+  # e.g. running old test modules that were in the stable release but
+  # have been removed from master. (See gh-2765, gh-2768.)  Using 'pip
+  # install' also has the advantage that it tests that numpy is 'pip
+  # install' compatible, see e.g. gh-2766...
+  - pip install .
 script:
   # We change directories to make sure that python won't find the copy
   # of numpy in the source directory.