setup: Tolerate running from different working directory.

setup.py

@@ -14,7 +14,10 @@ Topic :: Database
 Topic :: Software Development :: Libraries :: Python Modules
 """
 
-if not os.path.exists('mock.py'):
+base_path = os.path.dirname(__file__) or '.'
+
+mock_path = os.path.join(base_path, 'mock.py')
+if not os.path.exists(mock_path):
     import cStringIO, hashlib,subprocess,  urllib, zipfile
     x = 'pythonmock-0.1.0.zip'
     try:
@@ -25,7 +28,7 @@ if not os.path.exists('mock.py'):
     mock_py = zipfile.ZipFile(cStringIO.StringIO(x)).read('mock.py')
     if hashlib.md5(mock_py).hexdigest() != '79f42f390678e5195d9ce4ae43bd18ec':
         raise EnvironmentError("MD5 checksum mismatch downloading 'mock.py'")
-    open('mock.py', 'w').write(mock_py)
+    open(mock_path, 'w').write(mock_py)
 
 zodb_require = ['ZODB3>=3.10dev']
 
@@ -66,9 +69,10 @@ setup(
     license = 'GPL 2+',
     platforms = ["any"],
     classifiers=classifiers.splitlines(),
-    long_description = ".. contents::\n\n" + open('README.rst').read()
-                     + "\n" + open('CHANGELOG.rst').read(),
-    packages = find_packages(),
+    long_description = ".. contents::\n\n" +
+        open(os.path.join(base_path, 'README.rst')).read() + "\n" +
+        open(os.path.join(base_path, 'CHANGELOG.rst')).read(),
+    packages = find_packages(base_path),
     py_modules = ['mock'],
     entry_points = {
         'console_scripts': [