Add "# @no-test" tag to blacklist statements from test coverage analysis.

It can apply to either single statements:

    print "don't cover"; # @no-test

or a block of statements:

    if ( F )
        { # @no-test
        ...
        }

src/scan.l

@@ -216,6 +216,8 @@ ESCSEQ	(\\([^\n]|[0-7]+|x[[:xdigit:]]+))
 		}
 }
 
+#{OWS}@no-test.* return TOK_NO_TEST;
+
 #.*	/* eat comments */
 
 {WS}	/* eat whitespace */