Add Python 3.5.0b4

I copied and modified the file for beta 3.

plugins/python-build/share/python-build/3.5.0b4

@@ -0,0 +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_package "Python-3.5.0b4" "https://www.python.org/ftp/python/3.5.0/Python-3.5.0b4.tgz#e2f9ddb8eca441a5ae2bfccc015b61268d6bf612b3fd5b084d6ec2bf52c7d943" ldflags_dirs standard verify_py35 ensurepip