Merge pull request #998 from MikeMcQuaid/update-between-tags

update.sh: update to latest Homebrew/brew tag.

Library/Homebrew/brew.sh

-HOMEBREW_VERSION="0.9.9"
+HOMEBREW_VERSION="1.0.0"
 
 onoe() {
   if [[ -t 2 ]] # check whether stderr is a tty.

Library/Homebrew/cmd/update.sh

@@ -215,7 +215,18 @@ merge_or_rebase() {
 
   trap reset_on_interrupt SIGINT
 
-  REMOTE_REF="origin/$UPSTREAM_BRANCH"
+  if [[ "$DIR" = "$HOMEBREW_REPOSITORY" && -z "$HOMEBREW_NO_UPDATE_CLEANUP" ]]
+  then
+    UPSTREAM_TAG="$(git tag --list --sort=-version:refname | head -n1)"
+  fi
+
+  if [ -n "$UPSTREAM_TAG" ]
+  then
+    REMOTE_REF="refs/tags/$UPSTREAM_TAG"
+    UPSTREAM_BRANCH="v$UPSTREAM_TAG"
+  else
+    REMOTE_REF="origin/$UPSTREAM_BRANCH"
+  fi
 
   if [[ -n "$(git status --untracked-files=all --porcelain 2>/dev/null)" ]]
   then
@@ -337,7 +348,7 @@ EOS
     set -x
   fi
 
-  if [[ -z "$HOMEBREW_UPDATE_CLEANUP" ]]
+  if [[ -z "$HOMEBREW_UPDATE_CLEANUP" && -z "$HOMEBREW_UPDATE_TO_TAG" ]]
   then
     if [[ -n "$HOMEBREW_DEVELOPER" || -n "$HOMEBREW_DEV_CMD_RUN" ]]
     then