Add undo-tree to the default Prelude packages
Merge branch 'master' of github.com:bbatsov/prelude

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
Fix #264 - disable autoindent on yank for python-mode
Merge remote-tracking branch 'prelude/master'
manually added undo-tree