Fix regression in test `colon4.test'. * tests/colon4.test: Fix botched editing to `configure.in' that made the test useless. Since we are at it, improve comments and make grepping of generated Makefile.in slighty stricter. Regression introduced by change "Modernize, improve and/or extend tests `colon*.test" (Stefano Lattarini, 2010-08-08).