[tclwebtest] Infinite loop found in translate_entities

[Grzegorz A. H. <gr...@ti...>]

I've commited a test to selftest/entity.test which enters an infinite
loop.  This situation is found with the following real world test:

tclwebtest::do_request "http://validator.w3.org/check?uri=http://alleg.sourceforge.net/logos_03.es.html"

This prints an HTTP status of 200, but locks up in line 2405 of
tclwebtest.tcl, about 17 lines after the puts that prints the
HTTP status.