Fixing Time Machine Skippage

Time Machine has been skipping some folders on my work machine, and every simple trick I tried failed to make it back them up. Finally, I dug deep and found the problem: the OS X Extended Attributes for those folders contained this
The problem here is that these folders are part of an Xcode project, and it seems that Xcode is tagging them for exclusion. Not nice.
The “how to remove this” instructions came from
The salient bit from that article is this:

Use the xattr command. You can inspect the extended attributes:

$ xattr s.7z

and use the -d option to delete one extended attribute:

$ xattr -d s.7z
$ xattr s.7z