PaulL

Atlassian support and Git support have both pointed out that local and remote are consistent with the definition in the manual for difftool http://git-scm.com/docs/git-difftool.html.
So, what we have is, in the global .gitconfig file:
[diff]
tool = "sourcetree"
[difftool "sourcetree"]
cmd = ''C:/Users/Paul/AppData/Local/Programs/Git/bin/_LVCompareWrapper.sh'' "$REMOTE" "$LOCAL"
The associated wrapper script contents are:
#!/bin/bash
# Method to determine absolute path
# The -W parameter on the pwd command is necessary to return the Windows version of the path.
# Not using the -W parameter will result in a conversion of temp directory to a 'tmp' path meaningful only in the Linux # environment.
# Piping the result through tr '/' '' translates the forward slashes to backslashes.
# Windows understands forward slashes, but LVCompare.exe does not.
abspath () {
(
DIR=$(dirname "$1")
FN=$(basename "$1")
cd "$DIR"
printf "%s/%s" "$(pwd -W)" "$FN" | tr '/' ''
)
}
lvcompare="C:Program Files (x86)National InstrumentsSharedLabVIEW CompareLVCompare.exe"
local=$(abspath "$1")