Use the diff tool specified by <tool>.
Valid merge tools are:
kdiff3, kompare, tkdiff, meld, xxdiff, emerge, vimdiff, gvimdiff,
- ecmerge, diffuse, opendiff and araxis.
+ ecmerge, diffuse, opendiff, p4merge and araxis.
+
If a diff tool is not specified, 'git-difftool'
will use the configuration variable `diff.tool`. If the