git integration improvements

[lobneroO]

I have just set up comparePlus as my default git diff tool, so far I'm really happy with it.

There are two things that would make this even better:

1. (and probably the smaller request): mark which part of the (git) diff is the old version and which the new version. -> Since both files in a git diff are name the same and sometimes they are in temp folders, it is not immediately obvious, which of the two is belonging to which part of the git diff.

2. (and I don't know if this is even possible): add a 4-part merge :-)

Also, since it took my some time to set it up, perhaps it would be useful for others to document the git config entries necessary. I did it like this:

[diff]
tool = npp_compareplus

[difftool]
prompt = false

[difftool "npp_compareplus"]
cmd = \"C:\\Program Files\\Notepad++\\notepad++.exe\" -multiInst -nosession -pluginMessage=compare \"$REMOTE\" \"$LOCAL\"

On a sitenote, this didn't really work if I left out the -multiInst argument. It would open the diff, but it would close after a few seconds without me doing anything. Not sure if that's a bug.