auto merge of #13024 : brson/rust/issue-12799, r=thestinger

The only stage that can be installed from is 2 everywhere but windows,
3 on windows.

Lightly tested. Not actually tested on Windows, but I did confirm that a *similar* change fixed the problem on Windows.

Closes #12799
mk: Stop building OS X .pkg as part of 'make dist'

This doesn't work quite right yet (we need to build packages for all hosts)
and I'm not ready to turn on new dist artifacts yet, but I want to start doing
dry runs for 0.10, so I'm turning this off for now.
mk: Reorder definitions in dist.mk

Just to be more logical, put big headers between different installers
mk: Cleanup
mk: Make OS X .pkg for all arches
mk: Cleanup version handling and add support for nightly dists
mk: Put win installer in correct dir
mk: Add docs to dist prep

For integrating doc upload into the dist-snap process
mk: Add FIXME about making windows installer support all hosts
mk: Fix distcheck

Also, add more distcheck tests
mk: Wire up everything to dist and distcheck

Fix some misc bugs
mk: Fix location of man pages in prepare.mk