Always rebuild dist dir in "make dist" or install
auto merge of #559 : mbrubeck/cargo/make-install-fix, r=alexcrichton

This fixes an issue where `make dist` incorrectly does nothing after the source has changed and been rebuilt.  It also prevents `make install` from installing outdated files from the `dist` directory.
Allows bootstrapping win64 from win32 snapshot.
Remove triple = 'i686-pc-mingw32' once win64 snapshot is made.

Signed-off-by: Peter Atashian <retep998@gmail.com>
Merge commit '314d47749a79d0382eea1b710456b038a1ac84c0' into win64
Switch the URL from which nightlies are downloaded