To install, I uninstalled the old app with titanium backup.. Then reboot and install the apk (Gmail_v4.2.apk)
There you go - pinch to zoom in Gmail!
Works perfectly for me on XXDLIB
UPDATE: Tylwith added a CWN flashable zip - attached (gmail4.2.zip)
UPDATE 2: travp624 made an inverted colours apk - attached (Gmail4.2-signed-aligned.apk)
Android Police have an article about the new features here http://www.androidpolice.com/2012/10...tion-and-more/