Added empty options in setup.cfg

Setuptools removes them from the sdist, see psycopg#453

setup.cfg

@@ -7,24 +7,23 @@ define=
 
 # "pg_config" is required to locate PostgreSQL headers and libraries needed to
 # build psycopg2. If pg_config is not in the path or is installed under a
-# different name uncomment the following option and set it to the pg_config
-# full path.
-#pg_config=
+# different name set the following option to the pg_config full path.
+pg_config=
 
 # Set to 1 to use Python datetime objects for default date/time representation.
 use_pydatetime=1
 
 # If the build system does not find the mx.DateTime headers, try
-# uncommenting the following line and setting its value to the right path.
-#mx_include_dir=
+# setting its value to the right path.
+mx_include_dir=
 
 # For Windows only:
 # Set to 1 if the PostgreSQL library was built with OpenSSL.
 # Required to link in OpenSSL libraries and dependencies.
 have_ssl=0
 
-# Statically link against the postgresql client library.
-#static_libpq=1
+# Set to 1 to statically link against the postgresql client library.
+static_libpq=0
 
 # Add here eventual extra libraries required to link the module.
-#libraries=
+libraries=

setup.py

@@ -381,6 +381,11 @@ def finalize_linux(self):
 
     def finalize_options(self):
         """Complete the build system configuration."""
+        # An empty option in the setup.cfg causes self.libraries to include
+        # an empty string in the list of libraries
+        if self.libraries is not None and not self.libraries.strip():
+            self.libraries = None
+
         build_ext.finalize_options(self)
 
         pg_config_helper = PostgresConfig(self)
@@ -521,7 +526,7 @@ def is_py_64():
     mxincludedir = parser.get('build_ext', 'mx_include_dir')
 else:
     mxincludedir = os.path.join(get_python_inc(plat_specific=1), "mx")
-if os.path.exists(mxincludedir):
+if mxincludedir.strip() and os.path.exists(mxincludedir):
     # Build the support for mx: we will check at runtime if it can be imported
     include_dirs.append(mxincludedir)
     define_macros.append(('HAVE_MXDATETIME', '1'))