The way you Git ignore watching/tracking a particular dir/file. you just run this:
$ git update-index --assume-unchanged <file>
Now how do you undo it so they are watched again? (Let's call it un-assume.)
In order to get undo/show dir's/files that are set to assume-unchanged run this:
$ git update-index --no-assume-unchanged <file>
In order to get a list of dir's/files that are assume-unchanged run this:
$ git ls-files -v|grep '^h'