Corrections related to pip and archiving downloads:
- pip has long supported archiving source downloads (through the
--download-cache option)
- it seems pip 1.4 may not always archive previously built wheels properly and thus will rebuild them even though it shouldn't need to (https://github.com/pypa/pip/issues/855)
- pip 1.4's wheel support is initially aimed at Windows users, since they're the least likely to be able to handle installation from source, and there's less platform variety to cope with than there is across multiple versions of OS X and the huge variety of Linux distributions