Fixes CVE-2014-8121, CVE-2015-1781 and two unnumbered problems (apparently).
All these commits should be contained in the 2.22 release,
but we don't want that yet due to unresolved locale incompatibilites.
Now development stuff is propagated from the first output,
and userEnvPkgs from the one with binaries.
Also don't move *.la files (yet). It causes problems, and they're small.
- there were many easy merge conflicts
- cc-wrapper needed nontrivial changes
Many other problems might've been created by interaction of the branches,
but stdenv and a few other packages build fine now.
