clean up setup.py according to 9cfaf4a

- cython added to setup_requirements
  - setuptools will call easy_install to install it
  - all other build requirements, excluding numpy, will be resolved by pip
- do not parse requirements.txt
  - requirements should be the real runtime requirements
- fail gracefully when missing numpy
  - scipy will be resolved by pip from install_requires

setup.py

@@ -34,24 +34,10 @@ with open('skimage/__init__.py') as fid:
 with open('requirements.txt') as fid:
     INSTALL_REQUIRES = [l.strip() for l in fid.readlines() if l]
 
-# development versions do not have the cythonized files
-if VERSION.endswith('dev'):
-    SETUP_REQUIRES = [r for r in INSTALL_REQUIRES if r.startswith('cython')]
-else:
-    INSTALL_REQUIRES = [r for r in INSTALL_REQUIRES
-                                         if not r.startswith('cython')]
-    SETUP_REQUIRES = []
-
-
-# list requirements for PyPI
-REQUIRES = [r.replace('>=', ' (>= ') + ')'
-                      for r in INSTALL_REQUIRES + SETUP_REQUIRES]
+# requirements for those browsing PyPI
+REQUIRES = [r.replace('>=', ' (>= ') + ')' for r in INSTALL_REQUIRES]
 REQUIRES = [r.replace('==', ' (== ') for r in REQUIRES]
-
-
-# do not attempt to install numpy and scipy until they have eggs available
-INSTALL_REQUIRES = [r for r in INSTALL_REQUIRES
-                                     if not r.startswith(('scipy', 'numpy'))]
+REQUIRES = [r.replace('[array]', '') for r in REQUIRES]
 
 
 def configuration(parent_package='', top_path=None):
@@ -73,9 +59,17 @@ def configuration(parent_package='', top_path=None):
 
 
 if __name__ == "__main__":
-    # purposely fail loudly if numpy or scipy are not available
-    from numpy.distutils.core import setup
-    import scipy
+    # purposely fail if numpy is not available
+    # other dependecies will be resolved by pip (install_requires)
+    try:
+        from numpy.distutils.core import setup
+    except ImportError:
+        print('To install scikit-image from source, you will need numpy.\n' +
+              'Install numpy with pip:\n' +
+              'pip install numpy\n'
+              'Or use your operating system package manager. For more\n' +
+              'details, see http://scikit-image.org/docs/stable/install.html')
+        sys.exit(1)
 
     setup(
         name=DISTNAME,
@@ -105,8 +99,9 @@ if __name__ == "__main__":
         ],
 
         configuration=configuration,
-        setup_requires=SETUP_REQUIRES,
         install_requires=INSTALL_REQUIRES,
+        # install cython when running setup.py (source install)
+        setup_requires=['cython>=0.21'],
         requires=REQUIRES,
         packages=setuptools.find_packages(exclude=['doc']),
         include_package_data=True,