Fix build problem of Stackless 3.3.5 (refs #250)

plugins/python-build/share/python-build/stackless-3.3.5

@@ -1,3 +1,3 @@
 require_cc
 install_package "readline-6.3" "http://ftpmirror.gnu.org/readline/readline-6.3.tar.gz#56ba6071b9462f980c5a72ab0023893b65ba6debb4eeb475d7a563dc65cafd43" standard --if has_broken_mac_readline
-install_package "stackless-335-export" "http://www.stackless.com/binaries/stackless-335-export.tar.bz2#6558d1cb8c768ad95339fb9ca8b23106ce54c03ae67e9f75a84334d08489d240" ldflags_dirs standard verify_py33 ensurepip
+install_package "stackless-dev-stackless-c856cc204b1c" "https://bitbucket.org/stackless-dev/stackless/get/v3.3.5-slp.tar.bz2#197b41ccd7ec998ff612c67df9b8eb827a58f4eda715ca034c43c94bf17d5c0f" ldflags_dirs standard verify_py33 ensurepip