Update setup.py for from source builds without cython.

Test sdist builds on travis.
Include pxd/pyx files on sdist distributables.
Resolves #98

.travis.yml

@@ -27,6 +27,9 @@ script:
   - nosetests --with-coverage --cover-package=pssh
   - flake8 pssh
   - cd doc; make html; cd ..
+  # Test building from source distribution
+  - python setup.py sdist
+  - cd dist; pip install *; cd ..
 after_success:
   - codecov
 jobs:

MANIFEST.in

@@ -1,3 +1,5 @@
 include versioneer.py
 include pssh/_version.py
 recursive-exclude tests *
+include pssh/native/*.c
+include pssh/native/*.pyx

setup.py

@@ -20,7 +20,6 @@
 import versioneer
 
 try:
-    from Cython.Build import cythonize
     from Cython.Distutils.extension import Extension
     from Cython.Distutils import build_ext
 except ImportError:
@@ -45,10 +44,12 @@
     # 'libeay32', 'ssleay32',
     'Ws2_32', 'libssh2', 'user32']
 
+
+ext = 'pyx' if USING_CYTHON else 'c'
 _comp_args = ["-O3"] if platform.system() != 'Windows' else None
 extensions = [
     Extension('pssh.native._ssh2',
-              sources=['pssh/native/_ssh2.pyx'],
+              sources=['pssh/native/_ssh2.%s' % ext],
               include_dirs=["libssh2/include"],
               libraries=_libs,
               extra_compile_args=_comp_args,