[Fix #437] Always set $TMPDIR
Do not substitute /tmp since $TMPDIR is always set
Add the RubyGems bin directory to PATH on other Unix systems

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
[Fix #436] Remove Bombich rsync references
Revert "[Fix #436] Remove Bombich rsync references"

This reverts commit 20655c8b66907ff3cc879a8cbe7b82173b597e33.
[Fix #436] Update link to Bombich rsync
Rename archive module functions
Merge branch 'master' of https://github.com/sorin-ionescu/prezto