Fix rex tests so that they don't cause a cascading error.

[salspaugh]

Most tests have been changed from:

parsed = splparser.parser.parse("search foo")
parsed.print_tree()

to:

splparser.parser.parse("search foo").print_tree()

Because the former way causes errors to cascade. Rex tests need to be changed to look like the latter to address this bug too.

[salspaugh]

@keroro824 Don't forget to close your issues next time.