Allow building against system wide lz4 library

MANIFEST.in

@@ -1,2 +1,4 @@
 include README.rst
 include src/*.h
+include tests/*.py
+exclude tests/*.pyc

setup.py

@@ -2,10 +2,57 @@
 
 
 from setuptools import setup, find_packages, Extension
+import subprocess
+import os
 
 VERSION = (0, 7, 0)
 VERSION_STR = ".".join([str(x) for x in VERSION])
 
+# Check to see if we have a lz4 library installed on the system and
+# use it if so. If not, we'll use the bundled library. If lz4 is
+# installed it will have a pkg-config file, so we'll use pkg-config to
+# check for existence of the library.
+pkg_config_exe = os.environ.get('PKG_CONFIG', None) or 'pkg-config'
+cmd = '{0} --exists liblz4'.format(pkg_config_exe).split()
+liblz4_found = subprocess.call(cmd) == 0
+
+if liblz4_found:
+    # Use system lz4, and don't set optimization and warning flags for
+    # the compiler. Specifically we don't define LZ4_VERSION since the
+    # system lz4 library could be updated (that's the point of a
+    # shared library).
+    lz4mod = Extension('lz4',
+                       [
+                           'src/python-lz4.c'
+                       ],
+                       extra_compile_args=[
+                           "-std=c99",
+                           "-DVERSION=\"%s\"" % VERSION_STR,
+                       ],
+                       libraries=['lz4'],
+    )
+else:
+    # Use the bundled lz4 libs, and set the compiler flags as they
+    # historically have been set. We do set LZ4_VERSION here, since it
+    # won't change after compilation.
+    lz4mod = Extension('lz4',
+                       [
+                           'src/lz4.c',
+                           'src/lz4hc.c',
+                           'src/python-lz4.c'
+                       ],
+                       extra_compile_args=[
+                           "-std=c99",
+                           "-O3",
+                           "-Wall",
+                           "-W",
+                           "-Wundef",
+                           "-DVERSION=\"%s\"" % VERSION_STR,
+                           "-DLZ4_VERSION=\"r130\"",
+                       ]
+    )
+
+
 setup(
     name='lz4',
     version=VERSION_STR,
@@ -16,22 +63,8 @@
     url='https://github.com/steeve/python-lz4',
     packages=find_packages('src'),
     package_dir={'': 'src'},
-    ext_modules=[
-        Extension('lz4', [
-            'src/lz4.c',
-            'src/lz4hc.c',
-            'src/python-lz4.c'
-        ], extra_compile_args=[
-            "-std=c99",
-            "-O3",
-            "-Wall",
-            "-W",
-            "-Wundef",
-            "-DVERSION=\"%s\"" % VERSION_STR,
-            "-DLZ4_VERSION=\"r119\"",
-        ])
-    ],
-    setup_requires=["nose>=1.0"],
+    ext_modules=[lz4mod,],
+    tests_require=["nose>=1.0"],
     test_suite = "nose.collector",
     classifiers=[
         'Development Status :: 5 - Production/Stable',