Replaced all 'typeset' and 'typeset -i' calls by 'local', as adviced on:

    https://wiki.ubuntu.com/DashAsBinSh

Went back from making use of the specific Bourne shell construct 'typeset
-i' for easy integer calculations (typeset -i foo=123; foo=foo+456;) to a
more compatible way (local foo=123; foo=$((foo+456)); )

The 'typeset -f' call has been replaced by a call to 'type', effectively
not testing for existence of a declared *function*, but testing for
existence of a declared *something*. You have to sacrifice sometimes in
order to be more portable.
diff --git a/git-flow-release b/git-flow-release
index 556af28..329a5e1 100644
--- a/git-flow-release
+++ b/git-flow-release
@@ -40,9 +40,9 @@
 	DEFINE_boolean verbose false 'verbose (more) output' v
 	parse_args "$@"
 
-	typeset release_branches
-	typeset current_branch
-	typeset short_names
+	local release_branches
+	local current_branch
+	local short_names
 	release_branches=$(echo "$LOCAL_BRANCHES" | grep "^$PREFIX")
 	if [ -z "$release_branches" ]; then
 		warn "No release branches exist."
@@ -53,20 +53,20 @@
 	short_names=$(echo "$release_branches" | sed "s ^$PREFIX  g")
 
 	# determine column width first
-	typeset -i width=0
-	typeset branch
+	local width=0
+	local branch
 	for branch in $short_names; do
-		typeset -i len=${#branch}
+		local len=${#branch}
 		width=$(max $width $len)
 	done
-	width=width+3
+	width=$(($width+3))
 
-	typeset branch
+	local branch
 	for branch in $short_names; do
-		typeset fullname=$PREFIX$branch
-		typeset base=$(git merge-base "$fullname" "$DEVELOP_BRANCH")
-		typeset develop_sha=$(git rev-parse "$DEVELOP_BRANCH")
-		typeset branch_sha=$(git rev-parse "$fullname")
+		local fullname=$PREFIX$branch
+		local base=$(git merge-base "$fullname" "$DEVELOP_BRANCH")
+		local develop_sha=$(git rev-parse "$DEVELOP_BRANCH")
+		local branch_sha=$(git rev-parse "$fullname")
 		if [ "$fullname" = "$current_branch" ]; then
 			printf "* "
 		else
@@ -77,7 +77,7 @@
 			if [ "$branch_sha" = "$develop_sha" ]; then
 				printf "(no commits yet)"
 			else
-				typeset nicename=$(git rev-parse --short "$base")
+				local nicename=$(git rev-parse --short "$base")
 				printf "(based on $nicename)"
 			fi
 		else
@@ -190,9 +190,9 @@
 	# try to tag the release
 	# in case a previous attempt to finish this release branch has failed,
 	# but the tag was set successful, we skip it now
-	typeset tagname=$VERSION_PREFIX$VERSION
+	local tagname=$VERSION_PREFIX$VERSION
 	if ! gitflow_tag_exists "$tagname"; then
-		typeset opts="-a"
+		local opts="-a"
 		flag sign && opts="$opts -s"
 		[ "$FLAGS_signingkey" != "" ] && opts="$opts -u '$FLAGS_signingkey'"
 		[ "$FLAGS_message" != "" ] && opts="$opts -m '$FLAGS_message'"