git-mergeto does non-fast-forward merge from the current branch onto the specified branch.

git-mergeto

#!/bin/sh -e

BRANCH=`git symbolic-ref HEAD 2>/dev/null | cut -d/ -f3`
if [ x$1 = 'x' ]; then
  TO='master'
else
  TO=$1
fi
git checkout $TO
git merge $BRANCH --no-ff
git branch -d $BRANCH