check: don't use multi-line coloring for the report

check: don't use multi-line coloring for the report

"less -R" can't handle multi-line coloring as it is done for the
check reports of the serial and parallel testsuite, because of
performance reasons.  Thus, color each line of the check report
by its own.

* lib/am/check.am (am__text_box): Accept colors for lines, and
color each line by its own.
[%?PARALLEL_TESTS%] $(TEST_SUITE_LOG): Let am__text_box handle
the line coloring.
[!%?PARALLEL_TESTS%] $(check-TESTS): Color each report line by
its own.
* THANKS: Update.