Not sure what happened with your .xml file, but I searched mine, and albums which are supposed to be marked "gapless" are, and others aren't. I recently imported a group of files, (crank calls), which I wanted to play back gapless. I knew Apple removed this useful setting in iTunes 11, and was disappointed to see it still hadn't been replaced in iTunes 12. I'm not sure why, but Apple seems to want to make iTunes more difficult to use with each new iteration. It's probably just a coincidence that this began after Steve was gone. Nevertheless, you can insert the line:
<key>Part Of Gapless Album</key><true/>
into your .xml file, and it seems to work. Just open up the '~/Music/iTunes/iTunes Library.xml' file in a good text editor, search for the album you wish to make gapless, and insert this line in the entry for each song between the sample rate and the artwork count. It will look like this:
<key>Bit Rate</key><integer>320</integer>
<key>Sample Rate</key><integer>44100</integer>
<key>Part Of Gapless Album</key><true/>
<key>Artwork Count</key><integer>1</integer>
<key>Persistent ID</key><string>CF7A2C287954B2C4</string>
It's a pain, to be sure, especially if it's a lot of tracks, but if you really want an album to play without Crossfade, this is what we're all stuck with now. I'm sure there's a good unix way to do this, but I haven't worked it out yet.
Obviously, when these tracks are played in a shuffled playlist with other tracks, the gapless flag won't be respected. Then again, if all the tracks were flagged as gapless, then it might. I haven't tested this.