I've upgraded git today and in its README file I found the following excerpt:
If you don't already have Tcl/Tk Aqua installed on your computer (most MacOS X installs have it), you will get this error message. To resolve it, simply go to the website for Tcl / Tk Aqua and download the latest version:
If you have an older version of Tcl / Tk Aqua, you'll benefit from upgrading. There have been many usability improvements since the version that comes shipped with MacOS X Leopard.
I tried the link and it redirects to Daniel A. Steffen LinkedIn page, who is the lead developer of Tcl/Tk for Mac, as far as I understand. I tried googling to find alternative links, but they all redirect to the same LinkedIn page. From this I gather that either this alternative version is already included in the Mac OS X, or there is some ongoing conflict. Can anybody enlighten the situation?