To install the GNU Autotools bundle for the first time simply run the follow commands in a Terminal session.
$ mkdir -p ~/Library/Application\ Support/TextMate/Bundles
$ cd ~/Library/Application\ Support/TextMate/Bundles
$ git clone git://github.com/cyphactor/gnuautotools-tmbundle.git GNU\ Autotools.tmbundle
To have TextMate reload its bundles after you have installed a bundle simply go to the Bundles menu select Bundle Editor and then select Reload Bundles.
To check for a new version and get the latest version after you have previously installed the bundle simply perform the following steps in a Terminal.
$ cd ~/Library/Application\ Support/TextMate/Bundles/GNU\ Autotools.tmbundle
$ git pull