Use Sublime Merge as a git mergetool

mergetoolwrapper.sh

#!/bin/bash
# A wrapper script to make sublime_merge work more nicely
# when used as a git-mergetool

WORKDIR=`git rev-parse --show-toplevel`
REAL_HOME="$HOME/"
# Replace a leading homedir with ~/ to match the window title
REAL_WORKDIR=${WORKDIR/"^$REAL_HOME"/"~/"}

sublime_merge $REAL_WORKDIR

# Wait here for safety, no idea how long launching
# and daemonizing can take
sleep 2

# List all the windows first
# Then look for all Sublime Merge windows
# Then check if there is one for our current work dir
while wmctrl -lx | grep "sublime_merge.Sublime_merge" | grep -q "$REAL_WORKDIR"; do sleep 1; done
exit 0

sublime_merge.gitconfig

[merge]
	tool = sublime_merge
[mergetool]
	keepBackup = false
[mergetool "sublime_merge"]
	trustExitCode = false
	cmd = "/path/to/mergetoolwrapper.sh"

Note that smerge itself is beginning to become a git mergetool.