Add a --with-mock switch to the setup.py script.

The switch enables the optional compilation of the mock C extension, which
depends on libmockspotify.

setup.py

@@ -3,6 +3,7 @@
 from distutils.core import setup, Extension
 import os
 import re
+import sys
 
 def get_version():
     init_py = open('spotify/__init__.py').read()
@@ -23,6 +24,16 @@ def fullsplit(path, result=None):
         return result
     return fullsplit(head, [tail] + result)
 
+def with_mock():
+    """
+    Checks wether the user wants to build the mockmodule (off by default).
+    """
+    try:
+        sys.argv.remove('--with-mock')
+        return True
+    except ValueError:
+        return False
+
 # Compile the list of packages available, because distutils doesn't have
 # an easy way to do this.
 packages, data_files = [], []
@@ -88,6 +99,10 @@ def fullsplit(path, result=None):
     libraries=['mockspotify'],
 )
 
+modules = [spotify_ext]
+if with_mock():
+    modules.append(mockspotify_ext)
+
 setup(
     name='pyspotify',
     version=get_version(),
@@ -98,5 +113,5 @@ def fullsplit(path, result=None):
     url='http://pyspotify.mopidy.com/',
     packages=packages,
     data_files=data_files,
-    ext_modules=[spotify_ext, mockspotify_ext],
+    ext_modules=modules,
 )