Use `3.4` branch for `3.4-dev` (fixes #287)

plugins/python-build/share/python-build/3.4-dev

@@ -1,3 +1,3 @@
 #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_hg "Python-3.4-dev" "https://bitbucket.org/mirror/cpython" "default" standard verify_py34 ensurepip
+install_hg "Python-3.4-dev" "https://bitbucket.org/mirror/cpython" "3.4" standard verify_py34 ensurepip