Downgrade package if needed

[suside]

Actual:

root@lxc-test:/app# curd install Django==1.6.2 
root@lxc-test:/app# curd install Django==1.5.5 
root@lxc-test:/app# pip freeze | grep -i django==
Django==1.6.2

Expected:

root@lxc-test:/app# curd install Django==1.6.2 
root@lxc-test:/app# curd install Django==1.5.5 
root@lxc-test:/app# pip freeze | grep -i django==
Django==1.5.5

[clarete]

That's a bug in our cache detection. Curdling is too aggressive trying to always use already compiled binaries. Thanks for opening the issue!