Release finish squash parameter

Adding an optional (false by default) -S option to 'git flow release finish' to allow squashing
the commit

git-flow-release

@@ -45,7 +45,7 @@ PREFIX=$(git config --get gitflow.prefix.release)
 usage() {
 	echo "usage: git flow release [list] [-v]"
 	echo "       git flow release start [-F] <version> [<base>]"
-	echo "       git flow release finish [-Fsumpk] <version>"
+	echo "       git flow release finish [-FsumpkS] <version>"
 	echo "       git flow release publish <name>"
 	echo "       git flow release track <name>"
 }
@@ -193,6 +193,7 @@ cmd_finish() {
 	DEFINE_boolean push false "push to $ORIGIN after performing finish" p
 	DEFINE_boolean keep false "keep branch after performing finish" k
 	DEFINE_boolean notag false "don't tag this release" n
+    DEFINE_boolean squash false "squash release during merge" S
 
 	parse_args "$@"
 	require_version_arg
@@ -224,9 +225,15 @@ cmd_finish() {
 	if ! git_is_branch_merged_into "$BRANCH" "$MASTER_BRANCH"; then
 		git checkout "$MASTER_BRANCH" || \
 		  die "Could not check out $MASTER_BRANCH."
+        if noflag squash; then
 		    git merge --no-ff "$BRANCH" || \
 		        die "There were merge conflicts."
 		        # TODO: What do we do now?
+        else
+            git merge --squash "$BRANCH" || \
+                die "There were merge conflicts."
+            git commit
+        fi
 	fi
 
 	if noflag notag; then
@@ -253,9 +260,16 @@ cmd_finish() {
 
 		# TODO: Actually, accounting for 'git describe' pays, so we should
 		# ideally git merge --no-ff $tagname here, instead!
+        if noflag squash; then
 		    git merge --no-ff "$BRANCH" || \
 		        die "There were merge conflicts."
 		        # TODO: What do we do now?
+        else
+		    git merge --squash "$BRANCH" || \
+		        die "There were merge conflicts."
+		        # TODO: What do we do now?
+            git commit
+        fi
 	fi
 
 	# delete branch