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