I just bought a new Mac with OS X Lion and I checked in the Terminal what version of git is installed by default. I got the answer
git --version
> git ver
I prefer not to alter the path hierarchy, but instead deal with git specifically...knowing that I'm never going to use old git to do what new git will now manage. This is a brute force solution.
NOTE: I installed XCode on Yosemite (10.10.2) clean first.
I then installed from the binary available on git-scm.com.
$ which git
/usr/bin/git
$ cd /usr/bin
$ sudo ln -sf /usr/local/git/bin/git
$ sudo ln -sf /usr/local/git/bin/git-credential-osxkeychain
$ sudo ln -sf /usr/local/git/bin/git-cvsserver
$ sudo ln -sf /usr/local/git/bin/git-receive-pack
$ sudo ln -sf /usr/local/git/bin/git-shell
$ sudo ln -sf /usr/local/git/bin/git-upload-archive
$ sudo ln -sf /usr/local/git/bin/git-upload-pack
$ ls -la
(you should see your new symlinks)