More hygiene in installer:

* change uninstall.sh to run under zsh, so we have access to better
  file globbing, string substitution, and $ZDOTDIR
* remove additional oh-my-zsh data files in uninstall
* remove unneeded `source ~/.zshrc` in uninstall
* remove bogus `. ~/.zshrc` at end of install.sh: it would just read it
   in the `sh` process running install.sh right before exiting, so it
   would have no effect aside from sometimes kicking out syntax errors.

tools/uninstall.zsh

@@ -0,0 +1,33 @@
+#!/usr/bin/env zsh
+
+echo "Removing $ZSH"
+if [[ -d $ZSH ]]; then
+  rm -rf $ZSH
+fi
+
+echo "Removing Oh My Zsh data files"
+if [[ -z $SHORT_HOST ]]; then
+  SHORT_HOST=${HOST/.*/}
+fi
+setopt null_glob
+rm -fv ~/.zsh-update ${ZDOTDIR:-${HOME}}/.zcompdump-${SHORT_HOST}-*
+
+
+echo "Looking for original zsh config..."
+if [ -f ~/.zshrc.pre-oh-my-zsh ] || [ -h ~/.zshrc.pre-oh-my-zsh ]; then
+  echo "Found ~/.zshrc.pre-oh-my-zsh -- Restoring to ~/.zshrc";
+
+  if [ -f ~/.zshrc ] || [ -h ~/.zshrc ]; then
+    ZSHRC_SAVE=".zshrc.omz-uninstalled-`date +%Y%m%d%H%M%S`";
+    echo "Found ~/.zshrc -- Renaming to ~/${ZSHRC_SAVE}";
+    mv ~/.zshrc ~/${ZSHRC_SAVE};
+  fi
+
+  mv ~/.zshrc.pre-oh-my-zsh ~/.zshrc;
+
+else
+  echo "Switching back to bash"
+  chsh -s /bin/bash
+fi
+
+echo "Thanks for trying out Oh My Zsh. It's been uninstalled."