Upgrade distribute to the latest stable version of setuptools

'distribute' is the ancestor of 'setuptools', and many packages require
setuptools to be installed.

Upgrade of MySQL-python from 1.2.4 to 1.2.5 is required because of an
incompatibility with setuptools>0.7.

common/lib/capa/setup.py

@@ -4,5 +4,5 @@ setup(
     name="capa",
     version="0.1",
     packages=find_packages(exclude=["tests"]),
-    install_requires=["distribute>=0.6.28"],
+    install_requires=["setuptools"],
 )

common/lib/xmodule/setup.py

@@ -54,7 +54,7 @@ setup(
     version="0.1",
     packages=find_packages(exclude=["tests"]),
     install_requires=[
-        'distribute',
+        'setuptools',
         'docopt',
         'capa',
         'path.py',