pin pip version to 1.5.6 for python 3.1.5 (fixes #351)

plugins/python-build/share/python-build/3.1.5

@@ -1,3 +1,4 @@
 #require_gcc
 install_package "readline-6.3" "http://ftpmirror.gnu.org/readline/readline-6.3.tar.gz#56ba6071b9462f980c5a72ab0023893b65ba6debb4eeb475d7a563dc65cafd43" standard --if has_broken_mac_readline
-install_package "Python-3.1.5" "http://python.org/ftp/python/3.1.5/Python-3.1.5.tgz#d12dae6d06f52ef6bf1271db4d5b4d14b5dd39813e324314e72b648ef1bc0103" ldflags_dirs standard verify_py31 ensurepip
+install_package "Python-3.1.5" "http://python.org/ftp/python/3.1.5/Python-3.1.5.tgz#d12dae6d06f52ef6bf1271db4d5b4d14b5dd39813e324314e72b648ef1bc0103" ldflags_dirs standard verify_py31 ez_setup
+install_package "pip-1.5.6" "https://pypi.python.org/packages/source/p/pip/pip-1.5.6.tar.gz#b1a4ae66baf21b7eb05a5e4f37c50c2706fa28ea1f8780ce8efe14dcd9f1726c" python